THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 


GIFT  OF 


Prof.   W.   B.   Rising 


A  COMPENDIOUS  MANUAL 


QUALITATIVE  CHEMICAL  ANALYSIS, 


BY 


CHARLES  W.  ELIOT  AND  FRANK  IL   STORER. 


REVISED,  WITH  THE  CO-OPERATION  OF  THE  AUTHORS, 


.   RIFLE Y  NICHOLS, 

Professor  of  General  Chemistry  in  the  Massachusetts  Institute  of  Technology. 


NEW    YORK: 
D.    VAN    NOSTKAND,    PUBLISHER, 

23  MURRAY  STREET  AND  27  WARHEX  STRBBT. 

1872. 


Entered,  according  to  Act  of  Congress,  in  the  year  1872,  by 

C.  W.  ELIOT,  F.  H.  STOKER  and  W.  R.  NICHOLS, 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


Boston  i 
Stereofypcd  and  Printed  by  Alfred  Mudge  tf  Son. 


PREFACE. 


TIIK  authors  have  endeavored  to  include  in  this  short  treatise 
enough  of  the  theory  and  practice  of  qualitative  analysis  "  in  the 
wet  way,"  to  bring  out  all  the  reasoning  involved  in  the  subject, 
and  to  give  the  student  a  firm  hold  upon  the  general  principles 
and  methods  of  the  art.  It  has  been  their  aim  to  give  only  so 
much  of  mechanical  detail  as  is  essential  to  an  exact  comprehension 
of  the  methods  and  to  success  in  the  actual  experiments.  Hence, 
the  multiplication  of  different  tests  or  processes,  having  essentially 
the  same  object,  has  been  purposely  avoided.  For  the  same  reason 
none  of  the  rare  elements  are  alluded  to.  The  manual  is  intended 
to  meet  the  wants  of  the  general  student,  to  whom  the  study  is 
chiefly  valuable  as  a  means  of  mental  discipline  and  as  a  compact 
example  of  the  scientific  method  of  arriving  at  truth.  To  profes- 
sional students  who  wish  to  make  themselves  expert  analysts,  this 
little  book  offers  a  logical  introduction  to  the  subject,  an  outline 
which  is  trustworthy  as  far  as  it  goes,  but  which  needs  to  be  filled  in 
and  enlarged  by  the  subsequent  use  of  some  more  elaborate  treatise  as 
a  book  of  reference.  Prof.  Johnson,  of  Yale,  has  supplied  this  need 
with  his  excellent  edition  of  Fresenius's  comprehensive  manual. 

The  authors  believe  that  they  have  put  into  the  following  pages 
as  much  of  inorganic  qualitative  analysis  as  is  useful  for  training, 
and  also  as  much  as  the  engineer,  physician,  agriculturist,  or  lib- 
erally educated  man  needs  to  know.  The  book  has  been  written 
for  the  use  of  classes  in  the  Institute  of  Technology,  who  have 
already  studied  the  authors'  "Manual  of  Inorganic  Chemistry."  It 
is  simply  an  implement  devised  to  facilitate  the  giving  of  thorough 

237536 


iv  PEEFACE. 

instruction  to  large  classes  in  the  laboratory.  It  is  the  authors' 
practice  to  examine  their  classes  orally  every  four  or  five  exercises, 
in  order  to  secure  close*  attention  to  the  reasoning  of  the  subject. 
With  this  exception,  the  subject  is  studied  exclusively  in  the  labor- 
atory, tools  in  hand.  Fifty  laboratory  exercises  of  two  hours  each 
have  proved  sufficient  to  give  their  classes  a  mastery  of  the  subject 
as  it  is  presented  in  this  manual. 

It  is  scarcely  necessary  to  say  that  this  little  work  is  a  compila- 
tion from  well-known  authorities,  among  which  may  be  particularly 
mentioned  the  works  of  Galloway,  Will,  Fresenius,  and  Nort^icote 
&  Church. 

BOSTON,  April,  1869.  ' 


PKEFACE  TO  THE  REVISED  EDITION. 


IN  this  revised  edition,  undertaken  with  the  advice  and  consent 
of  the  authors,  such  alterations  and  additions  have  been  made  as 
have  been  suggested  by  the  use  of  the  book  with  a  number  of 
classes  in  the  laboratory. 

W.   R.   N. 

BOSTON,  July,  1872. 


TABLE  OF  CONTENTS. 


Introduction.     Qualitative    analysis    defined.     Scope    of  this    manual. 

Identifying  compounds.    Division  of  the  subject 1-3 

PART  I. 

Chapter  I.    Example  of  the  separation  of  two  elements.     Division  of 

twenty-four  metallic  elements  into  seven  classes.       ......       4-16 

Chapter  II.    Class  I.    Chlorides  insoluble  in  water  and  acids.    Lead. 

Silver.    Mercury 17-20 

Chapter  III.  Class  II.  Sulphides  insoluble  in  water,  dilute  acids  and 
alkalies.  Mercury.  Lead.  Bismuth.  Copper.  Cadmium.  The  pre- 
cipitation of  Classes  II  and  III 21-28 

Chapter  IV.  Class  III.  Sulphides  insoluble  in  water  or  dilute  acids, 
but  soluble  in  alkaline  solutions.  Arsenic.  Antimony.  Tin.  [Gold 
and  Platinum.] 29-36 

Chapter  V.  Class  IV.  Hydrates  insoluble  in  water,  ammonia-water, 
and  solutions  of  ammonium  salts.  Simultaneous  precipitation  of  some 
salts  which  require  an  acid  solvent.  Treatment  of  the  precipitate,  pro- 
duced by  ammonia-water.  Chromium.  Aluminum.  Manganese.  Iron. 
Separation  of  Class  IV  from  Classes  II  and  III.  The  original  condi- 
tion of  iron.  The  use  of  chloride  of  ammonium.  Interference  of  or- 
ganic matter 37-46 

Chapter  VI.  Class  V.  Sulphides  insoluble  in  water  and  in  saline  or 
alkaline  solutions.  Manganese.  Zinc.  Nickel.  Cobalt.  Separation 
of  Class  V  from  Class  IV 47-52 

Chapter  VII.  Class  VI.  Carbonates  insoluble  in  water,  ammonia-water 
and  saline  solutions.  Barium.  Strontium.  Calcium.  Separation  of 
Class  VI  from  the  preceding  classes 53-58 

Chapter  VIII,  Class  VII.  Three  common  metallic  elements  not  com- 
prised in  the  preceding  classes.  Magnesium.  Sodium.  Potassium. 
Table  for  the  separation  of  the  seven  classes  of  the  metallic  elements.  .  59-63 

Chapter  IX.  General  tests  for  the  non-metallic  elements.  The  classes  of 
salts  treated  of.  General  reactions  for  acids.  Metallic  elements  to  be 
first  detected.  The  barium  test.  The  calcium  test.  The  silver  test. 
Nitrates,  chlorates  and  acetates .  64-73 


CONTENTS. 


Chapter  X.  Special  tests  for  the  non-metallic  elements.  Effervescence. 
Carbonates.  Cyanides.  Sulphides.  Sulphites.  Hyposulphites.  Chro- 
mates.  A^senites  and  Arseniates.  Sulphates.  Phosphates.  Oxalates. 
Tartrates.  Borates.  Silicates.  Fluorides.  Chlorides.  Bromides. 
Iodides.  Nitrates.  Chlorates.  Acetates 74-S3 


PART  II. 

Treatment  of   substances    of  unknown   composition.     General 

observations.    Husbanding  material 83 

Chapter  XI.  Treatment  of  a  salt,  mineral  or  other  non-metallic  solid. 
Order  of  procedure.  .  .  .  Preliminary  examination  in  the  dry  way. 
Closed-tube  test.  Gases  or  vapors/  to  be  recognized.  Sublimates.  Re- 
duction test.  Metallic  globules/  .  .  .  Dissolving  a  salt,  mineral  or 
other  non-metallic  solid,  free  from  organic  matter.  Dissolving  in  water. 
Dissolving  in  acids.  .  .  .  Treatment  of  solutions  obtained.  An 
aqueous  solution :  neutral,  acid,  alkaline.  An  acid  solution.  .  .  . 
Examination  of  the  solutions  for  the  non-metallic  elements.  .  .  . 
Table  of  solubilities.  .  .  .  Treatment  of  insoluble  substances. 
Fusions.  Treatment  of  the  fused  mass.  Decomposition  by  means 
of  carbonate  of  calcium  and  chloride  of  ammonium.  Fusion  with  acid 
sulphate  of  sodium.  Deflagration 90-120 

Chapter  XIX.     Treatment  of  a  pure  metal  or  alloy.     Action  of  nitric 

acid  on  metals.    Gold  test.    Platinum  test 121-124 

Chapter  XIII.  Treatment  of  liquid  substances.  Evaporation  test.  Test- 
ing with  litmus.  Testing  for  ammonia 125, 126 

'APPENDIX. 

Reagents.  Acids.  Sulphuretted  hydrogen.  Ammonia-water.  Ammo- 
nium salts.  Caustic  soda.  Sodium  salts.  Potassium  salts.  Nitrate  of 
silver.  Calcium  salts.  Barium  salts.  Acetate  of  lead.  Lead  paper. 
Magnesium  mixture.  Ferric  chloride.  Nitrate  of  cobalt.  Sulphate  of 
copper.  Chloride  of  tin.  Oxide  of  manganese.  Mercury  salts.  Bi- 
chloride of  platinum.  Zinc.  Solution  of  indigo.  Litmus  paper.  Starch 
paste.  Alcohol.  Water.  .  .  .  Solutions  of  known  composition. 
.  .  .  Utensils.  Reagent-bottles.  Test-tubes.  Test-tube  rack. 
Flasks.  Beakers.  Glass  funnels.  Filtering.  Filter-stand.  Rapid 
filtration.  Porcelain  dishes  and  crucibles.  Lamps.  Blast-lamps  and 
blowers.  Iron-stand.  Tripod.  Wire-gauze.  Triangle.  Water-bath. 
Sand-bath.  Blowpipes.  Platinum  foil  and  wire.  Pincers.  Platinum 
crucibles.  Wash-bottle.  Glass  tubing.  Stirring-rods.  Cutting  and 
cracking  glass.  Bending  and  closing  glass  tubes.  Blowing  bulbs. 
Caoutchouc.  Corks.  Gas-bottle.  Self-regulating  generator.  Mortars. 
Spatula} i-xlvi. 


QUALITATIVE   ANALYSIS. 


INTRODUCTION. 

1.  Qualitative  Analysis,  in  the  widest  sense  of  the  term, 
is  the  art  of  finding  out  the  elements  contained  in  compound 
substances.     The  general  definition  has  important  limitations 
in  practice.     In  the  first  place,  the  art,  as  commonly  taught, 
applies  almost  exclusively  to  mineral,  or  inorganic,  substances, 
and  touches  only  incidentally  upon  the  multifarious  compounds 
of  carbon  with  hydrogen,  oxygen,  nitrogen  and  a  few  other 
elements,  which  form  the  subject-matter  of  that  branch  of 
chemical    science    called    organic   chemistry.      Again,   the 
analysis  of  gases  constitutes  a  distinct  branch  of  analysis, 
requiring  methods  and  apparatus  of  its  own,  and  therefore 
to  be  most  advantageously  studied  by  itself.     These  deduc- 
tions made,  there  remains  the  analysis  of  inorganic  solids 
and  liquids,  which  is  in  fact  the  main  subject  of  qualitative 
analysis  in  the  present  technical  sense  of  the  term. 

Of  the  sixty-three  recognized  chemical  elements,  only  the 
thirty-four  most  important  are  embraced  in  the  systematic 
course  of  this  manual.  Means  of  detecting  a  few  other  less 
common  elements  are  incidentally  given ;  but  most  of  the 
elements  which  are  so  rare  as  to  be  at  present  of  little  inter- 
est except  to  the  professional  chemist  or  mineralogist  are  not 
alluded  to. 

2.  Some  previous  knowledge  of  general  chemistry  is  es- 
sential to  the  successful  study  of  qualitative  analysis.     It  is 
assumed  that  the  student  knows  something  of  the  common 

l 


2  IVENTIFYr        COMPOUNDS.  §  3 

elements  and  of  their  most  important  combinations,  that  he 
is  familiar  with  the  principal  laws  which  govern  chemical 
changes,  and  that  he  possesses  a  certain  skill  in  the  simplest 
manipulations.  The  tools  and  operations  employed  in  quali- 
tative anatysis  are  few  and  simple  ;  but  neatness,  method  in 
working  and  a  vigilant  attention  even  to  the  minutest  details, 
are  absolutely  essential.  As  the  various  substances  used  or 
produced  in  the  operations  of  analysis  will  not  be  particularly 
described,  the  careful  student  will  keep  at  hand  some  text- 
book on  general  chemistry,  to  which  he  can  constantly  refer 
to  refresh  his  recollection  of  the  formulae  and  physical  and 
chemical  properties  of  the  substances  referred  to.  It  should 
be  observed  that  it  is  often  very  difficult  —  in  fact,  impossible 
in  the  present  state  of  knowledge  —  to  express  in  exact 
equations  the  involved  or  obscure  reactions  which  occur  in 
complex  mixtures  during  the  operations  of  analysis.  It  is  a 
useful  exercise  for  students  to  write  out  in  equations  the 
simpler  chemical  changes  which  occur  in  analysis  ;  but  when 
the  attempt  is  made  to  put  a  complex  reaction  into,  numerical 
symbols,  the  equations  are  apt  to  express  either  more  than 
we  know,  or  less. 

3.  Although  the  detection  of  the  elements  contained  in 
compound  substances  is  the  ultimate  object  of  anatysis,  it  is 
only  by  exception  that  the  elements  themselves  are  isolated, 
and  recognized  in  their  uncombined  condition.  An  element 
is  generally  recognized  through  some  familiar  compound, 
whose  apparition  proves  the  presence  of  all  the  elements  it 
contains,  just  as  the  presence  of  any  word  upon  this  page 
makes  it  sure  that  the  letters  with  which  it  is  spelt  are  im- 
printed there.  If,  as  the  result  of  a  definite  series  of  opera- 
tions upon  some  unknown  body,  the  hydrated  oxide  of  iron 
be  produced,  no  iron  having  been  added  during  any  stage  of 
the  process,  the  proof  of  the  presence  of  iron  in  the  original 
body  is  quite  as  certain  as  if  the  gray  metal  itself  had  been 
extracted  -from  it.  If  some  well-known  sulphate,  like  sul- 
phate of  lead,  or  of  barium,  for  example,  result  from  a  series 


§  4  IDENTIFYING   COMPOUNDS.  3 

of  experiments  upon  some  unknown  mineral,  it  is  certain  that 
the  mineral  contained  sulphur ;  provided  only  that  no  sulphur 
has  been  introduced  in  any  of  the  chemical  agents  to  whose 
action  the  mineral  has  been  submitted. 

The  compounds  through  which  the  elements  are  recognized 
are  necessarily  bodies  of  known  appearance,  deportment  and 
properties.  They  are,  in  fact,  bodies  of  various,  though 
always  definite,  composition ;  oxides,  sulphides,  chlorides, 
sulphates  and  many  other  salts,  are  thus  made  the  means  of 
identifying  one  or  more  of  the  elements  which  they  contain. 
The  object  of  the  analyst  is  to  bring  out  from  the  unknown 
substance,  by  expeditious  processes  and  under  conditions 
which  admit  of  no  doubt  as  to  their  testimony,  these  identi- 
fying compounds,  with  whose  appearance  and  qualities  he  has 
previously  made  himself  acquainted.  As  he  follows  the 
course  of  experiments  laid  down  in  this  manual,  the  student 
will  gradually  acquire,  with  the  aid  of  frequent  references  to 
a  text-book  of  general  chemistry,  that  stock  of  information 
concerning  the  identifying  compounds  which  must  be  always 
ready  for  use  in  his  mind,  and  at  the  same  time  he  will  be 
made  familiar  with  the  character  of  the  methodical  processes 
which  secure  a  prompt  and  sure  testimony  to  the  elementary 
composition  of  the  substances  he  examines. 

4.  The  subject  is  treated  in  two  parts  or  divisions,  of 
which  the  first  contains  a  series  of  experiments  to  illustrate  a 
systematic  course  of  examination  for  substances  in  solution, 
when  once  that  solution  has  been  made ;  while  the  second 
treats  chiefly  of  the  preliminary  examination  of  solids  and 
the  means  of  bringing  them  into  solution,  and  indicates  the 
general  methods  to  be  pursued  in  the  actual  analysis  of  a 
substance  of  unknown  composition. 


PAET  FIRST. 


CHAPTER    I. 

DIVISION  OF  THE  METALLIC  ELEMENTS  INTO  CLASSES. 

5.  Example  of  the  Separation  of  two  Elements.  —  Put 
a  small  crystal  of  nitrate  of  silver  and  a  small  crystal  of 
sulphate  of  copper  into  a  test-tube  (Appendix,  §  65),  and 
dissolve  them  in  two  teaspoonfuls  of  water,  warming  the 
water  at  the  lamp  to  facilitate  the  solution.  Add  to  this 
solution  a  few  drops  of  dilute  chlorhydric  acid  (App.,  §  3). 
Shake  the  contents  of  the  tube  violently,  wait  until  the  curdy 
precipitate,  which  the  acid  produces,  has  separated  from  the 
liquid,  and  then  add  one  more  drop  of  chlorhydric  acid.  If 
this  drop  produces  an  additional  precipitate,  repeat  the  oper- 
ation until  the  new  drop  of  acid  produces  no  change  in  the 
partially  clarified  liquid.  Then,  and  not  till  then,  has  all  the 
silver  which  the  original  solution  contained  been  precipitated 
in  the  form  of  chloride  of  silver,  an  unemployed  balance  or 
excess  of  the  reagent,  chlorhydric  acid,  remaining  in  the  clear 
liquid  ;  this  liquid  can  be  readily  separated  by  nitration  from 
the  curdy  chloride. 

Shake  the  contents  of  the  test-tube,  and  transfer  them  as 
completely  as  possible  to  a  filter  (App.,  §  70),  supported  in  a 
very  small  glass  funnel  (App.,  §  69),  which  has  been  placed 
in  the  mouth  of  a  test-tube.  With  a  wash-bottle  (App.,  §  81) 
rinse  into  the  filter  that  portion  of  the  precipitate  which 
has  adhered  to  the  sides  of  the  first  test-tube.  When  the 


5  6  THE  TEEM  CLASS.  —  CLASS  I.  5 

filtrate  has  drained  completely  from  the  precipitate,  set  the 
test-tube  which  has  received  it  aside.  Wash  the  precipitate 
together  into  the  apex  of  the  filter  by  means  of  a  wash-bottle 
with  a  fine  outlet ;  and,  in  order  to  wash  out  the  soluble 
sulphate  of  copper  which  adheres  to  the  precipitate,  fill  the 
filter  full  of  water  two  or  three  times,  throwing  away  this 
wash-water  when  it  has  passed  through  the  filter. 

The  complete  separation  of  the  silver  and  copper  which 
were  mixed  in  the  original  solution  is  already  'accomplished  ; 
the  silver  is  on  the  filter  in  the  form  of  chloride  ;  the  copper 
is  in  the  clear,  bluish  filtrate.  This  speedy  and  effectual 
separation  of  the  two  elements  is  based  upon  the  fact  that 
chloride  of  silver  is  insoluble  in  water  and  acid  liquids,  and 
is,  therefore,  formed  when  chlorhydric  acid  is  added  to  a 
solution  containing  a  salt  of  silver  ;  chloride  of  copper,  how- 
ever, is  readily  soluble  in  water  and  acid  liquids,  and,  even 
if  formed  by  the  addition  of  chlorhydric  acid  to  a  solution 
of  a  compound  of  copper,  would  fail  to  manifest  itself  by 
appearing  as  a  precipitate.  It  is,  in  general,  true  that  when- 
ever, by  the  addition  of  a  reagent,  there  can  be  formed  in  any 
solution  a  compound  insoluble  in  the  liquids  present,  this 
compound  alwaj^s  separates  as  a  precipitate.  Such  differ- 
ences of  solubility  as  are  illustrated  by  the  case  of  the  chlor- 
ides of  silver  and  copper  are  the  chief  reliance  of  the  analyst. 

6.  Definition  of  the  term  "  Class."  Class  I.  —  In  the 
foregoing  experiment  only  two  elements  have  been  separat- 
ed. It  might  obviously  be  very  difficult,  if  not  impossible,  to 
find  a  special  reagent  for  every  element,  which  would  always 
precipitate  that  single  element  and  never  any  other.  Chlor- 
hydric acid,  for  example,  which  precipitates  silver  so  ad- 
mirably from  any  solution  containing  that  element,  is  capable 
of  eliminating  two  other  elements  under  like  conditions.  The 
lower  chloride  of  mercury  (mercurous  chloride  or  calomel)  is 
insoluble  in  water  and  weak  acids.  Chloride  of  lead  is 
sparingly  soluble  in  cold  water,  and  is  still  less  soluble  in 
water  acidulated  with  chlorhydric  acid.  The  chlorides  of  the 


6  DIVISION  INTO  CLASSES.  §  6 

other  metallic  elements  are  all  soluble  in  water  and  acids 
under  the  conditions  of  the  analytical  process. 

There  are  embraced  in  the  scope  of  this  manual  twenty- 
two  of  the  so-called  metallic  elements,  —  elements  whose 
hydrates  or  oxides  are  said  to  be  basic  in  their  character,  and 
are  collectively  designated  as  bases :  if  chlorhydric  acid  were 
added  in  proper  quantity  to  a  solution  imagined  to  contain 
all  these  elements,  three,  and  only  three,  of  the  twenty-two 
elements  would  be  precipitated  as  chlorides.  After  filtration 
and  washing,  a  mixture  of  chloride  of  silver,  chloride  of  lead 
and  mercurous  chloride  would  remain  upon  the  filter,  and  all 
the  other  elements  would  have  passed  as  soluble  compounds 
into  the  filtrate.  Silver,  lead  and  mercury,  the  three  ele- 
ments thus  separated  from  the  rest  by  this  well-marked 
reaction  with  chlorhydric  acid,  constitute  a  class,  the  first  of 
several  classes  into  which  the  metallic  elements  are  divided 
for  the  ends  of  qualitative  analysis.  Each  class  is  character- 
ized by  some  clear  reaction  which  suffices,  when  intelligently 
applied,  to  separate  the  members  of  any  one  class  from  the 
other  classes.  The  chemical  agent,  by  means  of  which  this 
distinctive  reaction  is  exhibited,  is  called  the  general  reag<  nt 
of  the  class.  Thus,  chlorhydric  acid  is  the  general  reagent  of 
the  first  class. 

This  division  of  the  elements  into  classes  renders  it  un- 
necessary to  find  means  of  separating  each  individual  element 
from  all  the  others.  In  the  systematic  course  of  an  analysis, 
the  classes  are  first  sought  for  and  separated ;  afterwards 
each  class  is  treated  by  itself  for  the  detection  of  its  individ- 
ual members.  It  is  an  incidental  advantage  of  this  division 
of  the  elements  into  classes  that,  when  the  absence  of  any 
whole  class  has  been  proved  by  the  failure  of  its  peculiar 
general  reagent  to  produce  a  precipitate  in  a  solution  under 
examination,  it  is  unnecessary  to  search  further  for  any  mem- 
ber of  that  class.  Much  time  is  thus  saved,  for  it  is  as  easy 
to  prove  the  absence  of  a  class  as  of  a  single  element.  The 
full  treatment  of  the  first  class  of  elements,  comprising,  as 


§  §7,  8  DIVISION  INTO  CLASSES.  7 

we  have  seen,  silver,  lead  and  mercury,  is  the  subject  of 
Chapter  II. 

7.  Experiment  to  Illustrate  the  Division  of  the  Me- 
tallic Elements  into  Classes.  —  We  proceed  to  demonstrate 
experimentally  the  chemical  facts  upon  which  rests  the  divis- 
ion of  the  other  metallic  elements  into  convenient  classes. 

Prepare  a  complex  solution,  by  mixing  together  in  a  small 
beaker  (App.,  §  68)  a  small  teaspoonful  of  each  of  the  fol- 
lowing solutions  (App.,  §  62),  viz. :  —  chloride  of  copper,  ar- 
senious  acid  in  chlorhydric  acid,  ferrous  chloride,  chloride  of 
zinc,  chloride  of  calcium,  chloride  of  magnesium  and  chloride 
of  sodium.  Dilute  the  mixture  thus  prepared  with  its  own 
bulk  of  water.  Should  any  turbidity  or  precipitate  appear, 
add  chlorhydric  acid,  little  by  little,  until  the  -solution  be- 
comes clear,  "this  solution  is  representative  ;  it  contains  at 
least  one  member  of  each  of  the  classes  of  elements  which 
remain  to  be  defined.  It  contains  no  member  of  the  first 
class  ;  but  we  may  consistently  suppose  that  the  members  of 
this  class  have  been  previously  precipitated,  as  in  the  fore- 
going experiment  (§  5),  and  that  an  excess  of  chlorhydric 
acid  remains  in  the  liquid. 

8.  Definition  of  Classes  II  and  III.  —  Pass  a  slow  current 
of  sulphuretted  hydrogen  (App.,  §  14)  from  a  gas-bottle  or 
self-regulating  generator  through  the  acid  liquid  in  the  beaker. 
This  operation  must  be  performed  either  out  of  doors  or  in  a 
current  of  air  sufficient  to  carry  the  excess  of  the  gas  away 
from  the  operator.     A  dense,  dark  colored  precipitate  will 
immediately  appear,  and  gradually  increase  in  bulk.     When 
the  gas  has  flowed  continually  for  five  or  ten  minutes  through 
the  liquid,  remove  the  beaker  from  the  source  of  the  gas  (or 
interrupt  the  stream  of  gas  if  a  self-regulating  generator  be 
employed) ,  stir  the  liquid  well,  and  blow  out  the  sulphuretted 
Irvdrogen  which  lies  in  the  beaker.     If  after  the  lapse  of  two 
or  three  minutes  the  liquid  smells  distinctly  of  sulphuretted 
hydrogen,  it  is  saturated  with  the  gas,  and  it  is  sure  that  the 
reagent  has  done  its  work.     If  the  liquid  does  not  retain  the 


8  DEFINITION  OF  CLASSES  II  AND  III.  §  8 

characteristic  odor,  the  gas  must  be  again  passed  through  it 
until  saturation  is  certainly  attained. 

In  order  to  obtain  still  further  assurance  of  the  saturation 
of  the  liquid,  it  is  often  well  to  take  the  first  portions  of  the 
filtrate  of  the  succeeding  paragraph  and  add  a  small  quantity 
of  sulphuretted  hydrogen  water  (App.,  §  15).  If  a  sufficient 
amount  of  the  gas  had  not  been  passed  into  the  liquid,  the 
addition  of  the  sulphuretted  hydrogen  water  would  cause  the 
appearance  of  a  precipitate.  In  such  a  case  the  filtered  por- 
tion must  be  returned  to  the  beaker  and  the  stream  of  gas 
again  passed  through  the  liquid. 

Pour  the  contents  of  the  beaker,  well  stirred  up,  upon  a 
filter  which  is  supported  over  a  test-tube  or  second  beaker. 
Rinse  the  first  beaker  once  with  a  teaspoonful  of  water,  and 
transfer  this  rinsing  water  to  the  filter,  allowing  the  filtered 
liquid  to  mix  with  the  original  filtrate.  Label*  this  filtrate 
"  Filtrate  from  II  and  III "  (classes),  and  preserve  it  for 
later  study. 

If  any  considerable  quantitjr  of  precipitate  has  adhered  to 
the  sides  of  the  original  beaker,  it  may  be  detached  and 
washed  onto  the  filter  by  means  of  a  sharp  jet  of  water  from 
the  wash-bottle.  The  precipitate,  as  it  lies  upon  the  filter, 
must  then  be  washed  once  or  twice  with  water  ;  the  wash-water 


*  The  student  should  at  once  make  it  a  rule  to  label  every  filtrate  or 
precipitate  which  he  has  occasion  to  set  aside,  even  for  a  few  moments.  A 
bit  of  paper  large  enough  to  carry  a  descriptive  symbol  or  abbreviation 
should  be  attached  to  the  vessel  which  contains  the  liquid  or  precipitate. 
Paper  gummed  on  the  back  or  the  small  labels  which  are  sold  already 
gummed  are  convenient  for  this  use. 

This  habit,  once  acquired,  will  enable  the  student  to  carry  on  simul- 
taneously without  error  or  confusion,  several  operations.  He  may  be 
throwing  down  one  precipitate,  washing  another,  filtering  a  third,  and 
dissolving  a  fourth  at  the  same  time,  and  the  four  processes  may  belong  to 
as  many  different  stages  of  the  analysis.  There  will  be  no  danger  of  error 
if  labels  are  faithfully  used  ;  and  a  great  deal  of  time  will  be  saved.  The 
unaided  memory  is  incapable  of  doing  such  work  with  that  full  certainty, 
admitting  of  no  suspicion  or  after-qualms  of  doubt,  which  is  alone  satisfy- 
ing, or  indeed  admissible,  in  scientific  research. 


§  8  CLASSES  II  AND  III.  9 

is  thrown  away.  The  washed  precipitate  consists  of  a  mix- 
ture of  sulphide  of  copper  (CuS)  and  tersulphide  of.  arsenic 
(As2S3).  The  fact  that  these  sulphides  are  precipitated  under 
the  conditions  of  this  experiment  proves  that  they  are  both 
insoluble  in  weak  acid  liquors.  They  are  also  both  insoluble 
in  water.  But  an  important  difference  between  the  two  sul- 
phides nevertheless  exists,  a  difference  which  affords  a  trust- 
worthy means  of  separating  one  from  the  other. 

When  the  water  has  drained  away  from  the  precipitate,  open 
the  filter  upon  a  plate  of  glass,  and  gently  scrape  the  precipi- 
tate off  the  paper  with  a  spatula  of  wood  or  horn.  Place  the 
precipitate  in  a  small  porcelain  dish  (App.,  §  73),  pour  over 
it  enough  of  a  solution  of  sulphydrate  of  sodium  (App.,  §  23) 
to  somewhat  more  than  cover  it,  and  heat  the  mixture  cau- 
tiously to  boiling,  stirring  it  all  the  time  with  a  glass  rod. 
The  quantity  of  sulphydrate  of  sodium  to  be  employed  varies, 
of  course,  with  the  bulk  of  the  precipitate  ;  in  this  case  two 
or  three  teaspoonfuls  will  probably  suffice.  It  is  very  undesi- 
rable to  use  an  unnecessarily  large  quantity  of  the  reagent  for 
reasons  that  will  hereafter  appear.  A  portion  of  the  original 
precipitate  remains  undissolved ;  but  a  portion  has  passed 
into  solution.  Filter  the  hot  liquid  again.  The  black  residue 
on  the  filter  is  sulphide  of  copper,  which  is  insoluble,  not  only 
in  water  and  weak  acids,  but  also  in  alkaline  liquids.  To  the 
filtrate,  collected  in  a  test-tube,  add  gradually  chlorhydric 
acid,  until  the  liquid  has  an  acid  reaction  on  litmus  paper 
(App.,  §  58).  A  yellow  precipitate  of  sulphide  of  arsenic  will 
appear  as  soon  as  the  alkaline  solvent  which  kept  it  in  so- 
lution is  destro3red.  The  sulphide  of  arsenic  differs  from  the 
sulphide  of  copper  in  that  it  is  soluble  in  alkaline  liquids. 

In  this  series  of  experiments  copper  and  arsenic  stand,  not 
as  isolated  elements,  but  as' representatives  of  classes.  The 
following  common  elements  have  sulphides  which  are  insoluble 
in  water,  weak  acids  and  alkaline  liquids  :  —  Lead,  mercury, 
bismuth,  cadmium  and  copper.  These  elements  constitute 
Class  II  in  our  system  of  analysis.  The  following  elements 


10  MEKCUKY  AND  LEAD.  §§  8,  9 

have  sulphides  which  are  insoluble  in  water  and  weak  acids, 
but  soluble  in  alkaline  liquids  :  —  Arsenic,  antimony,  tin  (and 
the  precious  metals  gold  and  platinum).  These  elements  con- 
stitute Class  III.  If  all  the  elements  of  both  groups  had 
been  present  in  the  original  solution,  one  class  might  have 
been  separated  from  the  other  by  the  same  process  emplo3Ted 
in  the  case  of  the  representative  elements,  arsenic  and  copper. 

The  question  may  naturally  suggest  itself,  how  it  happens 
that  lead  and  mercury  are  included  in  Class  II,  when  they  were 
both  precipitated  in  Class  I.  The  chloride  of  lead,  which  is 
thrown  down  by  chlorhydric  acid,  is  not  wholly  insoluble  in 
water  ;  hence  it  happens  that  the  lead  is  not  completely  pre- 
cipitated in  Class  I.  That  portion  of  the  lead  which  has 
escaped  precipitation  as  chloride  in  Class  I,  will  be  thrown 
down  as  sulphide  in  Class  II,  for  the  sulphide  of  lead  is  in- 
soluble in  water,  weak  acids .  and  alkalies.  In  regard  to 
mercury,  it  will  be  remembered  that  there  are  two  sorts  of 
mercury  salts,  mercurous  salts  and  mercuric  salts.  The  mer- 
curous  chloride,  Hg2Cl2,  (calomel)  is  insoluble  in  water ;  but 
the  mercuric  chloride,  HgCL,,  (corrosive  sublimate)  is  soluble 
in  water.  If,  therefore,  mercury  be  present  in  the  form  of 
some  mercurous  salt,  it  will  be  separated  as  mercurous  chloride 
in  Class  I.  If,  on  the  contrary,  it  be  present  in  the  form  of 
some  mercuric  salt,  it  will  be  separated  in  Class  II  as  mercuric 
sulphide  (HgS),  for  this  sulphide  is  insoluble  in  water,  weak 
acids  and  alkaline  liquids.  If  a  mixture  of  mercurous  and 
mercuric  salts  be  contained  in  the  original  solution,  mercury 
will  appear  both  in  Class  I  and  in  Class  II. 

The  treatment  of  Class  II  is  fully  discussed  in  Chapter  III. 
The  separation  of  Class  III  and  the  means  of  separating  the 
members  of  the  class,  each  from  the  others,  form  the  subject 
of  Chapter  IV. 

9.  Definition  of  Class  IV.  —  We  now  return  to  the  study 
of  the  filtrate  from  Classes  II  and  III.  Pour  the  liquid  into 
a  small  evaporating  dish,  and  boil  it  gently  for  five  or  six 
minutes  to  expel  the  sulphuretted  hydrogen  with  which  the 


§  9  DEFINITION  OF  CLASS  IV.  \\ 

fluid  is  still  charged.  To  make  sure  that  all  the  gas  is 
expelled,  hold  a  bit  of  white  paper  moistened  with  a  solution 
of  acetate  of  lead  (App.,  §  46)  over  the  boiling  liquid  ;  when 
the  paper  remains  white,  all  the  sulphuretted  hydrogen  is 
gone.  Next,  add  to  the  liquid  in  the  dish  ten  or  twelve 
drops  of  strong  nitric  acid  (App.,  §  4),  and  again  gently  boil 
the  liquid  for  three  or  four  minutes,  in  order  that  all  the  iron 
present  may  be  converted  into  ferric  salts.  Then  pour  the 
liquid  into  a  test-tube,  add  to  it  about  one  third  its  bulk  of 
chloride  of  ammonium  (App.,  §  19),  and  finally  add  ammonia- 
water  (App.,  §  16),  little  by  little, .until  the  mixture,  after 
being  well  shaken,  smells  decidedly  of  ammonia.  A  brownish- 
red  precipitate  of  hydrated  sesquioxide  of  iron  will  separate 
from  the  liquid.  Pour  the  contents  of  the  test-tube  upon  a 
filter,  rinse  the  tube  and  the  precipitate  once  with  a  little 
water,  and  preserve  the  whole  filtrate  for  subsequent  opera- 
tions. 

Two  other  inetals,  aluminum  and  chromium,  are  precip- 
itated, as  iron  has  here  been,  by  ammonia-water  under  the 
same  conditions  and  in  the  same  form,  viz.,  as  hydrates. 
These  three  elements,  therefore,  constitute  the  fourth  class, 
whose  treatment  forms  the  subject  of  Chapter  V.  The  hy- 
drates of  these  elements  are  insoluble  in  water,  even  in  the 
presence  of  sails  of  ammonium,  such  as  the  chloride  of  am- 
monium which  has  been  expressly  added,  and  the  nitrate  of 
ammonium  which  has  been  formed  during  the  neutralization 
of  the  acid  liquid.  The  student  may  be  curious  to  know 
why  the  presence  of  ammonium  salts  is  insisted  upon  before 
the  elements  of  this  class  are  thrown  down  by  ammonia-water. 
The  ammonium  salts  have  nothing  to  do  with  the  precipita- 
tion of  iron,  aluminum  and  chromium  ;  but  by  their  presence 
they  prevent  the  precipitation,  as  will  be  hereafter  explained, 
of  certain  other  elements  whose  hydrates,  though  but  slightly 
soluble  in  water,  are  dissolved  by  solutions  of  ammonium 
salts.  The  salts  of  ammonium  are  therefore  addecl  to  keep 
in  solution  certain  other  elements  which  otherwise  would 
encumber  Class  IV. 


12  DEFINITION  OF  CLASS  V.  §  10 

1O.  Definition  of  Class  V.  —  We  now  proceed  to  the 
examination  of  the  filtrate  from  the  precipitate  of  Class  IV. 
Bring  this  liquid  to  boiling  in  a  test-tube,  and  add  sulphy- 
drate  of  ammonium  ( App.,  §  17),  little  by  little,  to  the  boiling 
liquid  as  long  as  a  precipitate  continues  to  be  formed.  To 
make  sure  that  the  precipitation  is  complete,  shake  the  hot 
contents  of  the  test-tube  strongly,  and  then  allow  the  mixture 
to  settle  until  the  upper  portion  of  the  liquid  becomes  clear. 
Into  this  clear  portion  let  fall  a  drop  of  sulphydrate  of  am- 
monium ;  when  this  drop  produces  no  additional  precipitate, 
the  precipitation  is  complete.  Filter  off  the  whitish  precip- 
itate of  sulphide  of  zinc,  and  preserve  the  filtrate  for  further 
treatment.  It  sometimes  happens  that  this  precipitate  refuses 
to  settle  and  leave  the  upper  portion  of  the  liquid  sufficiently 
clear  to  test  in  the  manner  described  above ;  in  this  case  a 
small  portion  of  the  mixture  may  be  filtered  and  a  drop  of 
sulphydrate  of  ammonium  added  to  the  clear  filtrate  in  order 
to  determine  whether  the  precipitation  is  complete.  If  not, 
the  filtered  liquid  must  be  returned  to  the  flask  and  more  of 
the  reagent  added. 

The  element  zinc,  representing  a  new  class  of  elements,  is 
precipitated  under  the  conditions  of  the  above  experiment, 
because  its  sulphide,  though  soluble  in  dilute  acids,  is  insolu- 
ble in  alkaline  liquids.  The  metals  manganese,  nickel  and 
cobalt  resemble  zinc  in  this  respect,  and  these  four  elements 
therefore  form  a  new  class,  Class  V,  in  this  analytical  method. 
The  representative  sulphide  of  this  class  was  not  precipitated 
by  the  sulphuretted  hydrogen  when  that  reagent  was  em- 
ployed to  throw  down  the  members  of  the  Classes  II  and  III, 
because  the  solution  was  at  that  time  acid.  Again  it  was 
not  precipitated  with  Class  IV  by  the  ammonia-water,  because 
the  sulphuretted  hydrogen  with  which  the  solution  had  pre- 
viously been  charged,  was  expelled  by  boiling  before  the 
ammonia-water  was  added.  The  complete  treatment  of 
Class  V  forms  the  subject  of  Chapter  VI. 


§§  11,  12  DEFINITION  OF  CLASS    VII.  13 

11.  Definition  of  Class  VI.  —  Add  to  the  filtrate  from 
Class  V,  two  or  three  teaspoonfuls  of  carbonate  of  ammo- 
nium (App.,  §  18)  and  boil  the  solution.    A  white  precipitate 
of  carbonate  of  calcium  will  be  produced.     After  boiling, 
allow  the  precipitate  to  settle  until  the  upper  portion  of  the 
liquid  is  comparatively  clear.     To  this  clarified  portion  add  a 
fresh  drop  of  carbonate  of  ammonium.     If  this  drop  produce 
an  additional  precipitate,  more  carbonate  of  ammonium  must 
be  added,  and  the  boiling  repeated.    To  the  partially  clarified 
liquid  add  again  a  drop  of  carbonate  of  ammonium.     This 
process  of  making  sure  of  the  complete  precipitation  of  the 
calcium  is  essentially  the  same  as  that  prescribed  in  precip- 
itating the  last  class,  and  is,  indeed,  of  general  application. 
When  the  precipitation  of  the  calcium  has  been  proved  to  be 
complete,  filter  the  whole  liquid,  and  receive  the  filtrate  in  a 
small  evaporating-dish.     Calcium  is  separated  in  the  form  of 
carbonate  under  these  circumstances,  because  this  carbonate 
is  almost  insoluble  in  weak  alkaline  liquids,  when  an  excess 
of  carbonate  of  ammonium  is  present.     The  allied  elements 
barium  and  strontium  behave  in  the  same  way,  so  that  these 
three  elements,  viz.,  barium,  strontium  and  calcium,  compose 
a  new  class  —  Class  VI,  whose  complete  treatment  is  set 
forth  in  Chapter  VII. 

12.  Definition  of  Class  VII. — Of  the  twenty-two  me- 
tallic elements,  which  were  to  be  classified  (§6),  only  three 
remain,  viz.,  magnesium,  sodium  and  potassium.     It  is  ob- 
vious that  these  three  elements  could  not  have  remained  in 
solution  through   all  the  operations  to  which  the  original 
liquid   has  been  submitted,  unless  their  chlorides  and  sul- 
phides had  been  soluble  in  weak  acids,  and  their  oxides  (or 
hydrates),  sulphides  and  carbonates   soluble  in  dilute  am- 
monia-water,  at  least    in  presence  of  dilute   solutions   of 
ammonium  salts.     It  is  a  fact  that  all  these  compounds  of 
sodium  and  potassium  are  soluble  in  water,  and  in  weak  acid, 
alkaline,  and  saline  solutions ;  the  magnesium  would  have 
been  partially  precipitated  in  Classes  IV,  V  and  VI,  but  for 

2 


14  SEPARATION  OF  CLASSES.  §§  12,  13 

the  presence  of  ammonium  salts  in  the  solution.  These  three 
elements  constitute  Class  VII. 

Evaporate  the  filtrate  from  Class  VI  until  it  is  reduced  to 
one  half  or  one  third  of  its  original  bulk.  Pour  a  small 
part  of  the  evaporated  filtrate  into  a  test-tube ;  add  a  little 
ammonia-water  and  a  teaspoonful  of  phosphate  of  sodium 
(A pp.,  §  26),  and  shake  the  contents  of  the  tube  violently. 
Sooner  or  later  a  crystalline  precipitate  will  appear.  This 
peculiar  white  precipitate  of  phosphate  of  magnesium  and 
ammonium  identifies  magnesium;  but  as  we  have  added  a 
reagent  containing  sodium,  the  filtrate  is  useless  for  further 
examination.  The  liquid  remaining  in  the  e vapor ating-dish 
is  then  evaporated  to  dry  ness,  and  moderately  ignited  until 
fuming  ceases.  All  the  ammoniacal  salts  which  the  solution 
contained  will  be  driven  off  by  this  means,  and  there  will 
remain  a  fixed  residue,  in  which  are  concentrated  all  the  salts 
of  magnesium  and  sodium  which  the  solution  contained.  In 
this  case  we  have  already  proved  the  presence  of  magnesium ; 
it  remains  to  indicate  briefly  the  nature  of  the  means  used  to 
detect  the  sodium. 

Dissolve  the  residue  in  the  dish,  or  a  portion  of  it,  in  three 
or  four  drops  of  water.  Dip  a  clean  platinum  wire  (App,, 
§79)  into  this  solution,  and  introduce  this  wire  into  the 
colorless  flame  of  a  gas  or  spirit-lamp  (App.,  §  74).  An 
intense  yellow  coloration  of  the  flame  demonstrates  the  pres- 
ence of  sodium.  A  violet  coloration  would  have  proved  the 
presence  of  potassium.  Magnesium  compounds,  when  pres- 
ent, have  no  prejudicial  effect  on  these  characteristic  colora- 
tions. The  means  of  detecting  each  member  of  this  last 
class  in  presence  of  the  others  will  be  found  described  in 
Chapter  VIII. 

13.  A  condensed  statement  of  the  classification  illustrated 
by  the  foregoing  experiments  is  contained  in  the  table  on 
the  next  page.  All  the  common  metallic  elements  are  em- 
braced in  it.  The  place  of  the  precious  metals  gold  and 
platinum  is  also  indicated.  The  classification  itself  would 


§13 


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16  SEPARATION  OF  CLASSES.  §§  14?  15 

not  be  essentially  different,  if  all  the  rare  elements  were 
comprehended  in  it.  The  general  subdivisions  would  be  the 
same,  although  some  of  them  would  embrace  many  more 
particulars. 

14.  It  is   essential  to  success   to  follow  precisely  the 
prescribed  order  in  applying  the  various  general  reagents. 
Class  I  would  go  down  with  Class  II,  were  chlorhydric  acid 
forgotten  as  the  first  general  reagent.     Class  II  would  be 
precipitated  in  part  with  Class  IV  and  in  part  with  Class  V 
if  sulphuretted  hydrogen  were  not  used  in  its  proper, place. 
A   large  number  of  the  members  of  the  first  five  classes 
would  be  precipitated  as  carbonates  with  Class  VI,  were  they 
not  previously  eliminated  by  the  systematic  application  of 
chlorhydric  acid,  sulphuretted  hydrogen,  ammonia-water  and 
sulphydrate  of  ammonium  in  the  precise  order  and  under  the 
exact  conditions  above  described.     It  should  be  noticed  that 
all  the  general  reagents  are  volatile  substances,  which  can  be 
completely  removed  by  an  evaporation  to  dryness  followed 
by  a  very  moderate  ignition. 

15.  The  series  of  experiments  just  completed  is  merely 
intended  to  demonstrate  the  principles  in  accordance  with 
which  these  twenty-two  common  elements  are  classified  for 
the  purposes  of  qualitative  analysis.     The  general  plan  is 
here  sketched;  the  practical  details,  essential  to  success  in 
the  conduct  of  an  actual  analysis,  will  be  given  hereafter. 


§§16,17  17 


CHAPTER  II. 

CLASS  I.  —  ELEMENTS  'WHOSE   CHLORIDES  ABE   INSOLU- 
BLE IN  WATER  AND  ACIDS. 

16.  Example  of  the  Precipitation  of  the  Members  of 
Class  I.  —  Place  in  a  test-tube  five  or  six  drops  of  a  tolerably 
concentrated   aqueous   solution   of  nitrate  of  silver   (A pp., 
§  62),  an  equal  quantity  of  a  solution  of  mercurous  nitrate 
and  two  teaspoonfuk  of  a  solution  of  nitrate  of  lead.     In 
case  the  solution  becomes  turbid  through  the  action  of  car- 
bonic acid  dissolved  in  the  water,  pour  in  one  or  two  drops 
of  nitric  acid  to  destroy  the  cloudiness. 

Add  dilute  chlorhydric  acid  to  the  solution,  drop  by  drop, 
and  shake  the  mixture  thoroughly  after  each  addition  of  the 
acid,  until  the  fresh  portions  of  the  latter  cease  to  form  any 
precipitate  on  coming  in  contact  with  the  comparatively  clear 
liquor  which  floats  above  the  insoluble  chlorides.  Finally, 
add  three  or  four  more  drops  of  the  acid  to  insure  the  pres- 
ence of  an  excess  of  it  in  the  solution. 

17.  Analysis  of  the  Mixed  Chlorides.  —  The  following 
method  of  separating  the  chlorides  of  lead,  silver  and  mer- 
cury, one  from  another,  depends  upon  the  facts  :  —  1st.  That 
chloride  of  lead,  though  but  little  soluble  in  cold  water,  dis- 
solves readily  in  boiling  water,  while  chloride  of  silver  and 
subchloride  of  mercury  (mercurous  chloride,  Hg2Cl2),  are  as 
good  as  insoluble  in  that  liquid ;  2d.  That  chloride  of  silver 
is  soluble  in  ammonia-water ;  and  3d.  That  mercurous  chlo- 
ride is  discolored  by  ammonia-water  without  dissolving. 

To  effect  the  separation :  —  Collect  upon  a  filter  the  pre- 
cipitate produced  by  chlorhydric  acid,  allow  it  to  drain,  and 
rinse  it  with  a  few  drops  of  cold  water.  Place  a  clean  test- 
tube  beneath  the  funnel  which  contains  the  filter  and  precip- 


18  SEPARATION  OF  LEAD.  §  17 

itate,  thrust  a  glass  rod  through  the  apex  of  the  filter,  and 
wash  the  precipitate  off  the  filter  into  the  test-tube  by  means 
of  a  wash-bottle  which  throws  a  fine  stream. 

Heat  the  mixture  of  water  and  precipitate  to  boiling,  then 
allow  the  precipitate  to  settle  and  pour  off  the  hot  liquor 
upon  a  new  filter,  taking  care  to  retain  the  precipitate  as  far 
as  possible  in  the  tube.  To  the  clear  filtrate  add  two  or 
three  teaspoonfuls  of  dilute  sulphuric  acid.  (App.,  §  9.)  A 
white  cloud  of  sulphate  of  lead  will  be  formed  in  the  midst  of 

Test  the  liquid.  In  case  the  precipitate  contains  a  large 
for  proportion  of  chloride  of  lead,  it  may  happen  that 

•Pk»  the  hot  water  will  take  up  so  much  of  it  that  crystals 
of  the  chloride  will  separate  from  the  clear  aqueous  solution 
as  it  becomes  cold,  or  that  the  liquor  will  be  rendered  cloudy 
by  the  deposition  of  numerous  small  particles  of  the  chloride. 

Pour  a  fresh  quantity  of  water  upon  the  precipitate  which 
was  retained  in  the  test-tube,  boil  the  mixture  and,  after 
allowing  the  precipitate  to  subside,  pour  the  nearly  clear 
liquid  upon  the  same  filter  as  before.  This  operation  of  boil- 
ing the  precipitate  with  successive  portions  of  water  is  per- 
formed in  order  to  insure  the  complete  removal  of  the  chloride 
of  lead ;  the  liquid  is  filtered  through  the  same  filter  in  order 
to  retain  any  particles  of  the  precipitate  which  fail  to  settle 
in  the  tube,  but  it  is  not  necessary  to  save  this  wash-water  as 
most  of  the  chloride  of  lead  was  obtained  in  the  filtrate  from 
the  first  boiling. 

After  the  mixed  precipitate  of  chloride  of  silver  and  mer- 
curous  chloride  has  been  thus  boiled  with  water  several  times, 
cover  it  with  several  teaspoonfuls  of  ammonia-water,  heat  the 
mixture  to  boiling,  and  pour  it  upon  the  filter  used  in  the  last 
paragraph :  the  filtrate  is  to  be  received  in  a  clean  test-tube. 
The  chloride  of  silver,  dissolved  by  the  ammonia-water,  will 
pass  into  the  filtrate,  while  the  mercurous  chloride  suffers  de- 
composition, and  is  converted  into  an  obscure  compound  of 
mercury,  chlorine,  nitrogen  and  hydrogen,  which  remains 
upon  the  filter  in  the  form  of  an  insoluble  black  or  gray 
powder. 


§§  17,  18  SILVER  AND  MERCURY.  19 

To  confirm  the  presence  of  silver,  add  to  the  filtrate  dilute 
nitric  acid  (App.,  §  5),  until  the  solution  will  redden  litmus 
paper :  the  chloride  of  silver  is  reprecipitated  un-      Test 
changed  as  soon  as  the  alkaline  solvent  is  neutral-       for 
ized.  Ag. 

To  confirm  the  presence  of  mercury,  the  metal  itself  may 
be  set  free  by  heating  the  dry  residue  with  carbonate  of  so- 
dium (App.,  §  24)  in  a  glass  tube.  To  ensure  the  success  of 
this  experiment,  wash  into  the  lowest  point  of  the  filter  the 
whole  of  the  black  residue.  As  soon  as  the  last  drops  of 
liquid  have  drained  from  the  filter,  dry  the  latter,  either  in  a 
dish  upon  a  water-bath,  or  by  spreading  it  open  upon  a  ring 
of  the  iron  stand  (App.,  §  76)  placed  high  above  a  small 
flame  of  the  gas-lamp.  When  the  precipitate  is  completely 
dry,  scrape  it  from  the  paper,  mix  it  with  an  equal  Test 
bulk  of  carbonate  of  sodium  previously  dried  over  for 
the  gas-lamp  on  platinum  foil  (App.,  §  79)  and  HS» 
transfer  the  mixture  to  the  bottom  of  a  glass  tube,  No.  4 
(App.,  §  82),  closed  at  one  end.  Then  wipe  out  the  inside  of 
the  tube  with  a  tuft  of  cotton  fixed  to  a  wire,  or  with  a 
twisted  slip  of  paper,  and  heat  the  closed  end  of  the  tube 
for  two  or  three  minutes  in  the  flame  of  a  gas-lamp.  A  sub- 
limate of  finely  divided  metallic  mercury  will  form  upon  the 
walls  of  the  tube ;  it  will  cohere  to  visible  globules  when 
scratched  with  a  piece  of  iron  wire. 

18.  An  outline  of  the  operations  described  in  the  forego- 
ing paragraphs  may  be  presented  in  tabular  form,  as  fol- 
lows :  — 


The  General  Reagent  (HC1)  of  Class  I  precipitates  PbCla,  AgCl 
and  Hg2Cl2.    When  the  precipitate  is  boiled  with  water  :  — 

PbCl2  goes  into 
solution.       Con- 
firm presence  of 
lead  by  precipita- 
tion of  sulphate 
of  lead. 

AgCl   and   Hg2Cl2  remain   undissolved.     On 
treating  the  mixture  with  ammonia-water  :  — 

AgCl  dissolves. 
Confirm  presence  of 
silver  with  nitric 
acid. 

A  black  compound  of  Hg 
remains  undissolved.  Con- 
firm presence  of  Hg  by 
isolating  the  metal. 

20  CLASS  I.  §  19 

19.  In  the  actual  analysis  of  a  solution  of  unknown  com- 
position, a  precipitate  might  under  certain  circumstances  be 
formed  on  the  addition  of  chlorhydric  acid,  even  in  the  ab- 
sence of  all  members  of  Class  I.  This  might  occur  in  case 
the  liquid  under  examination  contained  a  hyposulphite  ;  for 
this  class  of  salts  is  decomposed,  with  evolution  of  sulphu- 
rous acid  and  deposition  of  sulphur,  on  the  addition  of  the 
general  reagent  HC1  of  Class  I.  Some  sulphides  also  are 
decomposed  by  chlorhydric  acid,  with  deposition  of  sul- 
phur. A  gelatinous  white  precipitate  of  hydrated  silicic  acid 
might  also  be  formed  at  this  stage  in  certain  circumstances, 
as  will  be  explained  hereafter  (§§  69  &  86, 1.  c,  a). 


§§20,21  21 


CHAPTER    in. 

CLASS   II. -ELEMENTS   WHOSE    SULPHIDES   ABE   INSOL- 
UBLE IN  WATER,  DILUTE  ACIDS  AND  ALKALIES. 

20.  Example  of  the  Precipitation  of  the  Members  of 
Class  II.  —  Place    in    a  small    beaker   a  half  teaspoonful 
of  a  solution  of  each  of  the  following  substances  :  —  mercuric 
chloride  (corrosive  sublimate),  chloride  of  bismuth,  of  cad- 
mium, and  of  copper,  together  with  two  or  three  teaspoonfuls 
of  a  cold  aqueous  solution  of  chloride  of  lead.     Fill  the 
beaker  half  full  of  water,  and  add,  drop  by  drop,  enough 
strong  chlorhydric  acid  to  redissolve  the  basic  chloride  of 
bismuth  which  the  water  precipitates. 

Place  the  beaker  beneath  a  chimney  or  in  a  strong  draught 
of  air,  and  saturate  the  solution  with  sulphuretted  hydrogen 
gas.  To  determine  when  enough  sulphuretted  hydrogen  has 
been  passed  through  the  liquid,  remove  the  beaker  every  four 
or  five  minutes  from  the  source  of  the  gas,  blow  away  the  gas 
which  lies  in  the  beaker  above  the  liquid,  and  stir  the  latter 
thoroughly  with  a  glass  rod.  If,  after  the  lapse  of  two  or 
three  minutes,  the  liquid  still  smells  strongly  of  sulphuretted 
hydrogen,  it  is  saturated  with  the  gas  and  ready  to  be  filtered. 
But  in  case  no  persistent  odor  of  sulphuretted  hydrogen  is 
observed,  the  gas  must  be  passed  anew  through  the  liquor 
until  it  has  become  fully  saturated.  Since  some  of  the  sub- 
stances above  enumerated  are  thrown  down  more  quickly  by 
sulphuretted  hydrogen  than  the  others,  it  is  absolutely  neces- 
sary to  employ  the  reagent  in  excess  in  order  that  those  mem- 
bers of  the  class  which  are  least  easily  precipitated  may  not 
escape  detection. 

21.  Analysis  of  the  Mixed  Sulphides. —  The  following 
method  of  separating  the  members  of  Class  II  depends  upon 


22  SEPARATION  OF  CLASS  If.  §  21 

the  facts  :  —  1st.  That  mercuric  sulphide  is  insoluble  in  hot 
dilute  nitric  acid,  while  the  other  sulphides  are  converted 
thereby  into  soluble  nitrates.  2d.  That  sulphate  of  lead  is 
insoluble  in  acidulated  water,  while  the  sulphates  of  the  other 
members  of  the  class  are  soluble.  3d.  That  hydrate  of  bis- 
muth is  insoluble  in  ammonia-water,  while  the  hydrates  of 
cadmium  and  copper  are  soluble  in  that  liquid.  4th.  That 
hot  dilute  sulphuric  acid  converts  the  sulphide  of  cadmium 
into  the  soluble  sulphate  of  cadmium  while  sulphide  of  copper 
is  not  affected  by  this  reagent. 

To  effect  the  separation :  —  Collect  the  precipitated  sul- 
phides upon  a  filter ;  wash  the  precipitate  thoroughly  with 
water,  in  order  to  completely  remove  the  chlorhydric  acid 
which  adheres  to  it :  transfer  the  precipitate  to  a  small  porce- 
lain dish,  pour  upon  it  four  or  five  times  as  much  dilute  nitric 
acid  as  would  be  sufficient  to  cover  it,  and  boil  the  mixture 
during  two  or  three  minutes,  stirring  it  constantly  with  a 
glass  rod,  and  adding  water  or  dilute  nitric  acid  at  intervals 
to  replace  the  liquid  which  evaporates.  All  the  sulphides 
with  the  exception  .of  the  sulphide  of  mercury  are  decomposed 
and  the  several  elements  go  into  solution  as  nitrates ;  the 
sulphide  of  mercury,  mixed  with  some  free  sulphur  resulting 
from  the  decomposition  of  the  other  sulphides,  remains  undis- 
solved,  as  a  heavy  dark-colored  mass.  Decant  the  nitric  acid 
solution  into  a  filter,  collect  the  filtrate  in  a  second  porcelain 
dish,  and  evaporate  it  nearly  to  dryness  in  order  to  drive  off 
the  greater  part  of  the  free  nitric  acid  before  examining  it  for 
the  elements  supposed  to  be  contained  in  it. 

The  residue  insoluble  in  nitric  acid  which  was  left  in  the 
first  dish,  is  to  be  washed  with  water  in  order  to  remove  the 
adhering  solution.  This  may  generally  be  done  by  pouring 
water  into  the  dish,  allowing  the  precipitate  to  settle  and  then 
decanting  the  wash-water ;  it  is  sometimes  necessary,  how- 
ever, to  collect  the  precipitate  on  a  filter  and  wash  in  the 
ordinary  manner.  In  either  case  the  wash-water  is  thrown 
away  and  the  precipitate  is  boiled  in  the  porcelain  dish  with 
as  much  aqua  regia  (App.,  §  6)  as  will  barely  cover*  it. 


§  21  SEPARATION  OF  MERCURY.  23 

Dilute  the  acid  solution  obtained  with  an  equal  volume  of 
water,  remove  from  it,  by  filtration  or  otherwise,  any  particles 
of  free  sulphur  which  may  remain  undissolved,  and  add  to  it 
almost,  but  not  quite,  enough  ammonia-water  to  neutralize 
its  acidity.  In  case  of  the  accidental  addition  of  too  much 
ammonia-water,  manifested  by  the  appearance  of  a  precipi- 
tate and  by  the  alkaline  reaction  on  litmus,  the  solution  must 
be  made  just  acid  by  the  cautious  addition  of  nitric*  acid,  a 
drop  at  a  time.  Place  in  the  slightly  acid  solution  a  small 
bit  of  bright  copper  wire,  and  observe  that  metallic  mercury 
is  deposited  upon  the  copper  as  a  white  silvery  coating.  After 
the  lapse  of  ten  or  fifteen  minutes,  dry  the  wire  upon  Test 
blotting  paper,  drop  it  into  a  narrow  glass  tube  which  for 
has  been  sealed  at  one  end,  and  heat  it  at  the  lamp.  Hg. 
Metallic  mercury  will  sublime,  and  be  deposited  as  a  dull 
mirror  upon  the  cold  portions  of  the  glass.  By  scratching 
the  sublimate  with  the  point  of  a  bit  of  iron  wire,  the  metal 
may  be  made  to  collect  into  visible  globules.^ • "" 

When  the  greater  part  of  the  free  nitric  acid  has,  by  the 
aforesaid  evaporation,  been  driven  off  from  the  filtrate  which 
contains  the  mixed  nitrates  of  lead,  bismuth,  cadmium  and 
copper,  transfer  the  residual  liquor  to  a  test-tube,      Test 
mix  it  with  two  or  three  times  its  volume  of  dilute     -for 
sulphuric  acid,  and  leave  the  mixture  at  rest  during      ^b« 
fifteen  or  twenty  minutes.     Sulphate  of  lead  will-  be  thrown 
down  as  a  white  powder,  plainly  to  be  seen  in  the  test-tube, 
though  it  would  have  been  scarcely  visible  in  the  white  dish. 
.^""The  appearance  of  this  heavy  white  precipitate  under  these 
conditions  proves  conclusively  the  presence  of  lead  ;  in  any  case 
of  doubt  the  following  confirmatory  test  may  be  applied  :  — 

Collect  the  precipitate  upon  a  filter,  wash  it  with  water, 
transfer  it  to  a  test-tube,  pour  upon  it  two  or  three  times  its 
volume  of  a  solution  of  normal  chromate  of  potassium  (App., 
§  31),  and  heat  the  mixture  to  boiling.  The  white  sulphate 
of  lead  will  be  converted  into  yellow  chromate  of  lead,  with- 
ou£  dissolving,  and  the  characteristic  color  of  the  latter  may 
be  made  manifest  by  collecting  it  upon  a  filter,  and  washing 


24  SEPARATION  OF  BISMUTH.  §  21 

it  with  water  until  the  excess  of  chromate  of  potassium  has 
been  completely  removed. 

Collect  the  nitrate  from  the  sulphate  of  lead  in  a  small 
beaker,  and  add  to  it  ammonia-water  by  repeated  small  por- 
tions, taking  care  to  stir  the  liquid  thoroughly  after  each 
addition  of  the  ammonia,  until  a  strong  persistent  odor  of  the 
latter  is  perceptible.  The  hydrates  of  copper,  cadmium,  and 
bismuth  will  all  be  thrown  down  at  first,  but  the  hydrates  of 
copper  and  cadmium  will  redissolve  in  the  excess  of  ammonia- 
water,  and  hydrate  of  bismuth  will  alone  be  left  as  an  insol- 
uble precipitate. 

To  prove  that  this  precipitate  contains  bismuth  :  —  Collect 
it  upon  a  filter,  allow  it  to  drain,  and  dissolve  it  in  the  small- 
est possible  quantity  of  strong  chlorhydric  acid  poured  drop  by 
drop  upon  the  sides  of  the  filter  ;  carefully  evaporate  the  acid 

Test  solution  to  the  bulk  of  two  or  three  drops,  and  pour 
for  it  into  a  large  test-tube  nearly  full  of  water.  A 

Ei«  dense  milky  cloud  of  insoluble  basic  chloride  of  bis- 
•*nuth  will  appear  in  the  water.  Since  sulphate  of  lead  is  not 
absolutely  insoluble  in  water  which  contains  nitric  acid,  a 
slight  precipitate  of  hydrate  of  lead  might  be  produced  on 
the  addition  of  the  ammonia-water  even  when  no  bismuth 
was  present  in  the  solution.  To  prove  the  presence  of  bis- 
muth, the  oxychloride  must  always  be  carefulty  tested  for. 

The  blue  color  of  the  ammoniacal  filtrate  from  the  hydrate 
of  bismuth  indicates  the  presence  of  copper,  and  when  well 
defined  is  of  itself  a  sufficient  proof  of  the  presence  of  this 
element.  But  in  the  absence  of  a  marked  blue  coloration,  at 
this  stage,  copper  should  be  specially  tested  for  in  the  man- 
ner described  below. 

To  separate  the  cadmium  from  the  copper,  proceed  as  fol- 
lows :  —  Transfer  the  ammoniacal  filtrate  to  a  glass  flask, 
heat  it  to  boiling,  and  drop  into  the  boiling  liquid  sulphydrate 
of  ammonium  as  long  as  a  precipitate  continues  to  be  formed. 
In  order  to  be  sure  that  the  precipitation  is  complete,  remove 
the  flask  from  the  lamp  at  intervals,  shake  it  strongly,  and 
allow  its  contents  to  settle,  so  that  a  comparatively  cfear 


§  21  SEPARATION  OF  CADMIUM.  25 

liquid  may  appear  at  the  top,  and  into  this  clear  liquid  pour 
a  drop  of  the  sulphydrate. 

As  a  general  rule,  the  operations  of  boiling  and  agitating 
tend  to  increase  the  coherency  of  precipitates,  and  to  render 
them  in  some  sense  granular,  so  that  they  separate  completely 
from  the  liquid  in  which  they  form,  leaving  it  clear  and  sus- 
ceptible of  rapid  filtration. 

Collect  the  precipitate  upon  a  filter,  rinse  it  once  or  twice 
with  water,  and  allow  it  to  drain ;  then  transfer  the  precip- 
itate to  a  porcelain  dish  and  cover  it  liberally  with  dilute 
sulphuric  acid  (App.,  §  10),  made  by  mixing  one  part  by  meas- 
ure of  the  strong  acid  with  five  parts  of  water.  Heat  the  mix- 
ture until  it  actually  boils  ;  then  pour  the  boiling  liquor  upon 
a  filter,  and  collect  the  clear  filtrate  in  a  beaker.  By  hot 
dilute  sulphuric  acid  of  the  prescribed  strength,  sulphide  of 
cadmium  is  converted  into  sulphate  of  cadmium  which  dis- 
solves in  the  acid  liquid,  while  the  black  sulphide  of  copper 
remains  intact.  It  is  essential  that  the  mixed  precipitate  of 
sulphide  of  copper  and  sulphide  of  cadmium  do  not  remain 
upon  the  filter  for  any  great  length  of  time ;  for  in  such  a 
case  the  sulphide  of  copper  might  become  partially  oxydized 
and  dissolve  in  the  dilute  sulphuric  acid,  along  with  the 
sulphate  of  cadmium,  thus  obscuring  the  test  for  the  latter 
element. 

To  prove  the  presence  of  cadmium,  pass  sulphuretted  hy- 
drogen gas  into  the  acid  filtrate  after  it  has  been      Test 
diluted  with  an  equal  bulk  of  water,  and  observe       for 
that  the  liquor  immediately  becomes  cloudy  from      Cd. 
the  presence  of  minute  particles  of  sulphide  of  cadmium  of 
characteristic  yellow  color.     After  some  time1  this  precipitate 
will  collect  at  the  bottom  of  the  liquid. 

To  prove  the  presence  of  copper,  in  case  no  blue  coloration 
was  visible  in  the  filtrate  from,  hydrate  of  bismuth,  transfer 
the  black  precipitate,  insoluble  in  dilute  sulphuric  acid,  to  an 
evaporating-dish,  dissolve  it  in  a  few  drops  of  boiling,  concen- 
trated nitric  acid,  remove  and  wash  the  spongy  mass  of  sulphur 

which  is  set  free,  neutralize  the  nitric  acid  with  ammonia- 

3 


TREATMENT  OF  CLASS  II. 


§§21,22 


water,  acidify  the  solution  with  acetic  acid  (App.,  §  12), 
transfer  it  to  a  test-tube,  and  add  one  or  two  drops  of  a 
solution  of  ferrocyanide  of  potassium  (App.,  §  33).  A  pe- 

Test  culiar  reddish-brown  precipitate  of  ferrocyanide  of 
for  copper  will  fall  in  case  much  copper  be  present,  and 

^u»  even  when  the  proportion  of  copper  in  the  solution 
is  extremely  small,,  a  light  brownish-red  cloudiness  will  be 
produced. 

In  the  absence  of  copper,  yellow  sulphide  of  cadmium 
would  at  once  be  thrown  down  by  the  sulphydrate  of  ammo- 
nium, when  this  reagent  is  added  to  the  filtrate  from  the  hy- 
drate of  bismuth  ;  and  no  further  evidence  of  the  presence  of 
cadmium  would  be  required. 

22.  The  operations  above  described  may  be  presented  in 
tabular  form  as  follows  :  — 


The  General  Reagent  (H2S)  of  Class  II  precipitates  HgS,  PbS, 
Bi2S3,   CdS   and  CuS  (as  well  as  members  of  Class  III,  which 
are  subsequently  separated  by  solution  in  sulphydrate  of  sodium) 
The  precipitate  is  boiled  with  nitric  acid  :  — 

A  residue  of 
HgS,  mixed 
with    S,  re- 
mains. 
Confirm 
presence   of 
Hg  with 
copper  wire. 

Pb,  Bi,  Cd  and  Cu  go  into  solution  as  nitrates. 
On  adding  dilute  sulphuric  acid  to  the  concentrated 
solution  :  — 

PbSO4    is 
thrown 
down.  [Con- 
firm the 
presence  of 
Pb  by  con- 
verting 
PbSO4into 
PbCrO4.] 

The  sulphates  of  Bi,  Cd  and  Cu  remain 
in  solution.     On  adding  an  excess  of 
ammonia-  water  :  — 

Hydrate  of 
Bismuth  is 
thrown 
down.    Con- 
firm Bi  by 
precipitat- 
ing the  oxy- 
chloride. 

Compounds  of  Cd  and  of 
Cu    remain    in    solution. 
Throw    down     CdS    and 
CuS  with  (NH4)  HS,  and 
boil  with  dilute  sulphuric 
acid:  — 

CdSO4  goes 
into  solu- 
tion.    Con- 
firm pres- 
ence of  Cd 
by  precipita- 
tion of  CdS 

CuS  remains 
undissolved. 
Confirm  pres- 
ence of  Cu 
by  testing 
with  ferrocy- 
anide of  po- 
tassium. 

5  23  SEPARATION  OF  CLASSES  I  AND  II.  27 

23.  The  Method  of  Separating  Class  I  from  Class  II  has 
already  been  particularly  described  in  §  6.  It  should  be  ob- 
served, however,  that  even  if  no  member  of  Class  I  were 
present  in  the  mixture  to  be  analyzed,  it  would  still  be  neces- 
sary to  acidulate  the  liquid  with  chlorhydric  acid,  before  pass- 
ing the  sulphuretted  hydrogen,  in  order  to  prevent  the  precipi- 
tation of  members  of  Classes  IV  and  V,  and  to  secure  the 
complete  precipitation  of  members  of  Class  III. 

The  liquid  should  be  watched  attentively  when  the  stream 
of  sulphuretted  hydrogen  first  begins  to  flow  through  it,  since 
useful  inferences  may  often  be  drawn  from  the  various  phe- 
nomena which  present  themselves. 

a.  Thus,  the  formation  of  a  white  precipitate  which  after- 
wards changes  to  yellow,  orange,  brownish-red,  and  finally  to 
black,  as  the  liquid  gradually  becomes  saturated  with  the  gas, 
indicates  the  presence  of  mercuric  chloride.     The  white  pre- 
cipitate at  first  formed  is  a  compound  of  chloride  and  sul- 
phide of  mercury  (HgCl22HgS),  but  by  the  action  of  succes- 
sive portions  of  sulphuretted  Irydrogen,  the  composition  and 
appearance  of  the  precipitate  is  changed,  until  it  has  been 
completely  converted  into  black  sulphide  of  mercury. 

b.  If  the  precipitate  is  of  a  dull  red  color  at  first,  after- 
wards changing  to  black,  the  probable  presence  of  lead  is 
indicated  ;  for  sulphuretted  hydrogen  throws  down  from  solu- 
tions which  contain  much  free  chlorhydric  acid  a  red  com- 
pound of  chloride  of  lead  and  sulphide  of  lead,  which  is 
afterwards  decomposed,  with  formation  of  the  black  sulphide, 
when  the  solution  becomes  saturated  with  the  gas. 

c.  A  decided  bright  yellow  precipitate  would  indicate  the 
presence  of  cadmium,  arsenic  or  tin  ;  of  these  three,  cadmium 
is  distinguished  by  the  fact  that  its  sulphide  remains  undis- 
solved  when  the  precipitate  is  treated  with  sulphydrate  of 
sodium  to  separate  the  members  of  Class  III. 

But  even  from  solutions  which  contain  no  members  of 
Classes  II  or  III,  yellow-white  or  milky-white  precipitates  of 
free  sulphur  are  often  thrown  down;  for  sulphuretted 


28  SEPARATION  OF  CLASSES  II  AND  III.          §  23 

hydrogen  is  easily  decomposed,  with  deposition  of  sul- 
phur, by  a  variety  of  oxidizing  agents,  such  as  nitric, 
chromic  and  chloric  acids,  and  solutions  of  ferric  salts  and  of 
free  chlorine.  If  the  solution  under  examination  contained 
much  nitric  acid,  sulphuretted  hydrogen  would  have  to  be 
passed  through  it  for  a  long  time  to  destroy  the  acid,  before 
the  liquid  could  be  saturated  with  the  gas.  In  this  case  the 
sulphur  separates  as  a  tenacious  mass  of  dirty  yellow  color  ; 
but  in  mos't  instances,  notably  when  the  solution  contains  a 
ferric  salt,  the  sulphur  is  precipitated  in  the  form  of  exceed- 
ingly minute  particles,  which  impart  to  the  solution  a  pecu- 
liar milkiness  or  opalescence.  These  particles  are  so  fine  that 
they  pass  through  the  pores  of  filter  paper ;  they  cannot  be 
removed  by  filtration. 

If  the  original  solution  contains  a  chromate,  its  yellow  or 
reddish-yellow  color  will  be  changed  to  green  by  the  action 
of  sulphuretted  hydrogen  ;  for  the  chromate  is  reduced  to  the 
condition  of  sesquichloride  of  chromium  :  — 

2MCr04+10HCl+3H2S=Cr2Cle+3S+2MCl2+8H20. 

The  sulphur  is  set  free  in  the  form  of  the  minute  white 
particles  above  described,  and  remains  suspended  in  the 
green  liquid,  looking  not  unlike  a  green  precipitate. 

d.  The  immediate  formation  of  a  black  precipitate  indi- 
cates the  presence  of  copper  or  bismuth,  and  it  is  to  be  ob- 
served that  either  of  these  black  precipitates  would  obscure 
the  colors  of  the  other  sulphides  of  the  class,  and  conceal 
them  if  present. 

e.  If  no  precipitate  appears  even  when  the  liquid  has  be- 
come saturated  with  the  gas,  the  absence  of  every  member  of 
Classes  II  and  HI  is,  of  course,  to  be  inferred. 


§24  29 


•CHAPTER    IV. 


CLASS  HI.  -  ELEMENTS  WHOSE  SULPHIDES  ARE  INSOL- 
UBLE IN  WATER  OR  DILUTE  ACIDS,  BUT  SOLUBLE  IN 
ALKALINE  SOLUTIONS. 


24.  Example  of  the  Precipitation  of  the  Members  of 
Class  III.  —  Place  in  a  small  beaker  six  or  eight  drops  of 
solutions  of  the  chlorides  of  arsenic,  antimony  and  tin.  Pour 
in  enough  dilute  chlorhydric  acid  to  half  fill  the  beaker,  and, 
if  need  be,  a  sufficient  number  of  drops  of  strong  chlorhydric 
acid  to  dissolve  any  cloud  of  basic  chloride  of  antimony 
which  may  appear  in  the  liquor. 

Pass  sulphuretted  hydrogen  gas  through  the  solution,  in 
the  manner  described  in  §  20,  until  the  odor  of  the  gas  per- 
sists. Then  collect  the  precipitated  sulphides  upon  a  filter, 
and  rinse  the  precipitate  once  or  twice  with  water. 

In  the  analysis  of  any  complex  solution  of  unknown  com- 
position which  might  contain  one  or  all  of  the  members  of 
Class  III,  the  sulphides  of  this  class  would,  of  course,  all  be 
thrown  down  at  the  same  time  as  those  of  Class  II.  (Com- 
pare §§  8,  22.)  It  will  be  well,  therefore,  for  the  sake  of 
illustration,  for  the  student  to  dissolve  the  present  precipitate 
in  sulphydrate  of  sodium  in  order  that  he  may  begin  the 
treatment  of  Class  III  at  the  precise  point  a£  which  this  class 
would  be  encountered  in  an  actual  anatysis ;  namely,  with 
the  sulphides  of  the  class  in  alkaline  solution.  To  this  end, 
allow  the  washed  precipitate  to  drain,  spread  out  the  filter 
upon  a  plate  of  glass,  scrape  the  precipitate  from  the  paper 
with  a  small  spatula  of  platinum,  horn  or  wood,  and  transfer 
it  to  a  porcelain  dish.  Pour  upon  the  precipitate  two  or 
three  times  as  much  of  a  solution  of  sulphydrate  of  sodium 


30  ANALYSIS  OF  CLASS  III.  §  25 

as  would  be  sufficient  to  cover  it,  and  boil  the  mixture  very 
cautiously,  so  as  to  avoid  spattering.  The  precipitate  will 
soon  dissolve,  and  no  solid  matter  will  be  left  suspended  in 
the  solution,  excepting  a  few  fibres  of  the  filter  paper.  It  is 
such  a  solution  as  this  which  in  an  actual  analysis  is  examined 
for  members  of  Class  III. 

25.  Analysis  of  the  Mixed  Sulphides.  —  The  method 
here  given  of  separating  arsenic,  antimony  and  tin  depends  : 
—  1st.  Upon  the  oxidation  of  the  several  sulphides  by  means 
of  nitric  acid  and  nitrate  of  sodium,  and  the  conversion  of 
arsenic  into  a  compound  soluble  in  water  while  antimony  and 
tin  are  converted  into  insoluble  compounds ;  2d.  Upon  the 
fact  that  the  tin  in  the  compound  thus  formed  is  set  free  in 
the  metallic  state  when  this  compound  is  treated  with  zinc 
and  chlorhydric  acid,  while  the  antimony  under  similar  cir- 
cumstances is  in  part  reduced  to  metallic  antimony  and  in 
part  converted  into  antimoniuretted  hydrogen  ;  3d.  Upon  the 
solubility  of  tin  in  strong  chlorhydric  acid. 

To  effect  the  separation  ;  —  Add  strong  nitric  acid  to  the 
sulphydrate  of  sodium  solution  until  the  reaction  is  distinctly 
acid ;  a  precipitate  forms  which  consists  partly  of  the  sul- 
phides of  arsenic,  antimony  and  tin,  and  partly  of  sulphur 
from  the  decomposition  of  the  alkaline  sulphydrate.  With- 
out heeding  the  precipitate  which  separates,  evaporate  the 
acid  mixture  to  the  bulk  of  one  or  two  teaspoonfuls ;  then 
add  a  small  teaspoonful  of  nitrate  of  sodium  in  powder, 
evaporate  to  dryness  with  constant  stirring,  and  heat  the 
mass  until  it  fuses.  Pour  out  the  liquid  mass,  as  far  as  may 
be  possible,  upon  a  bit  of  cold  porcelain,  and  when  it  has 
cooled  somewhat,  transfer  it,  together  with  whatever  can  be 
detached  from  the  dish  in  which  the  fusion  was  made,  to  a 
clean  mortar  and  reduce  it  to  powder.  Return  this  powder 
to  the  porcelain  dish  and  when  the  dish  with  its  contents  is 
perfectly  cold  pour  in  several  teaspoonfuls  of  cold  water  and 
allow  the  mixture  to  stand,  stirring  it  from  time  to  time,  until 
that  portion  of  the  fused  mass  which  could  not  be  detached 


§  25  SEPARATION  OF  ARSENIC.  31 

from  the  dish  has  softened  and  is  in  part  dissolved ;  finally, 
filter  the  solution.  By  the  treatment  with  nitric  acid  and 
nitrate  of  sodium  the  arsenic  of  the  sulphide  of  arsenic  has 
been  converted  into  arseniate  of  sodium,  a  compound  which 
is  soluble  in  water  and  which  passes  into  the  filtrate  together 
with  the  excess  of  nitrate  of  sodium  and  some  sulphate  of 
sodium  formed  during  the  process.  The  antimony  has  been 
converted  into  antimoniate  of  sodium  and  the  tin  into  the 
binoxide ;  these  two  compounds  remain  on  the  filter  as  an 
insoluble  residue.  This  residue  is  examined  for  antimony 
and  tin  in  a  manner  presently  to  be  described ;  the  filtrate 
is  divided  into  two  portions  and  tested  for  arsenic  as  fol- 
lows :  — 

To  one  portion  add  a  few  drops  of  nitric  acid.  If  a  pre- 
cipitate appear  it  is  probably  a  hydrate  of  tin,  and  its 
appearance  is  due  to  the  fact  that  the  ignition  with  nitrate 
of  sodium  was  conducted  at  so  high  a  temperature  that  a 
portion  of  the  nitrate  of  sodium  was  converted  into  caustic 
soda,  and  this  acting  on  the  oxide  of  tin  formed  a  certain 
amount  of  soluble  stannate  of  sodium. 

The  precipitate,  if  any  appear,  is  to  be  filtered  off  and 
added  to  the  insoluble   residue  which  awaits  examination. 
To  the  clear  filtrate  add  a  few  drops  of  a  prepared  solution 
of  sulphate  of  magnesium  and  chloride  of  ammo-      Test 
mum   (App.,  §  47)  and  set  the  mixture   aside  for       for 
twelve  hours.     The  formation  of  a  white,  crystalline      As- 
precipitate  of  arseniate  of  ammonium  and  magnesium  is  evi- 
dence of  the  presence  of  arsenic. 

To  the  second  portion  of  the  solution  which  contains  the 
arsenic,  add  not  too  small  a  quantity  of  a  solution  of 
nitrate  of  silver  (App.,  §  39).  Test  the  mixture  with  litmus 
paper,  and  if  the  solution  is  not  already  acid,  add  dilute  nitric 
acid,  drop  by  drop,  until  the  reaction  is  just  acid.  On  the 
addition  of  the  nitrate  of  silver  a  precipitate  generally  falls 
even  in  the  absence  of  arsenic,  owing  to  the  fact  that  the 
nitrate  of  sodium  used  in  the  fusion  generally  contains  some 


32  SEPARATION  OF  ARSENIC.  §  25 

chloride  of  sodium.  This  white  precipitate  remains  after  the 
addition  of  the  nitric  acid,  and  is  to  be  removed  by  filtration. 
To  the  clear  filtrate  add  a  solution  of  acetate  of  sodium 
(App.,  §  27),  drop  by  drop,  until  the  mixture  smells  of  acetic 
acid  ;  a  red  or  brownish-red  precipitate  of  arseniate  of  silver 
appears.  The  acetate  of  sodium  is  added  because  the  arsen- 
iate of  silver  is  soluble  in  nitric  acid,  and  but  sparingly  solu- 
ble in  acetic  acid  unless  in  considerable  excess :  on  the  addi- 
tion of  acetate  of  sodium  to  the  liquid  containing  free  nitric 
acid,  there  was  formed  nitrate  of  sodium,  and  acetic  acid  was 
set  free.  It  sometimes  happens  when  the  solution  of  the 
fused  mass  contains  a  large  amount  of  arsenic  (as  in  the 
present  case),  that  the  precipitate  of  arseniate  of  silver  ap- 
pears immediately  on  the  addition  of  the  nitrate  of  silver. 
In  such  a  case,  of  course,  the  appearance  of  the  precipitate 
at  that  point  is  an  indication  of  the  presence  of  arsenic,  and 
the  subsequent  treatment  with  nitric  acid,  filtration,  and  addi- 
tion of  acetate  of  sodium  may  be  omitted.  Any  precipitate 
supposed  to  contain  arsenic  may  be  further  examined  by  con- 
verting the  arsenic  into  a  hydrogen  compound,  by  the  method 
known  as  Marsh's  test.  (See  Eliot  and  Storer's  Manual  of 
Inorganic  Chemistry,  pp.  259,  270  ;  see  also  the  test  for  an- 
timony below.)  This  method  is  applicable  to  the  detection 
of  very  minute  quantities  of  arsenic. 

The  insoluble  residue  containing  antimony  and  tin,  which 
was  left  on  the  filter,  is  washed  several  times  with  a  mixture 
of  equal  parts  of  alcohol  and  water,  and  then  transferred  to 
a  test-tube  or  porcelain  dish  and  warmed  with  strong  chlorhy- 
dric  acid.  Choose  a  cork  or  caoutchouc  stopper  provided 
with  two  holes,  which  fits  accurately  the  mouth  of  a  wide 
test-tube.  Fit  a  small  thistle-tube  to  one  of  the  holes,  and 
to  the  other  a  short  straight  tube  drawn  to  a  rather  fine  open 
point.  Put  a  fragment  or  small  strip  of  zinc  (App.,  §  56), 
together  with  a  bit  of  platinum  foil  into  the  tube,  cover  with 
water,  close  the  tube  with  the  perforated  stopper  and, 
through  the  thistle-tube  add  strong  chlorhydric  acid  in  small 


§  25  SEPARATION  OF  ANTIMONY.  33 

successive  portions.  After  hydrogen  has  been  generated 
freely  during  four  or  five  minutes  by  the  mixture  in  the 
tube,  and  all  the  air  originally  contained  in  the  latter  has 
been  expelled,  light  the  gas  issuing  from  the  pointed  glass 
tube,  and  pour  into  the  thistle-tube,  a  portion  at  a  time,  the 
mixture  of  strong  chlorhydric  acid  and  the  residue  containing 
antimony  and  tin,  or  the  solution  if  the  acid  has  dissolved 
the  residue  completely.  Hold  a  cold  porcelain  dish  in  the 
flame,  taking  care  to  shift  the  position  of  the  dish  frequently 
so  that  fresh  surfaces  of  porcelain  may  be  exposed  to  the 
burning  gas.  If  there  be  really  any  antimony  in  the  insolu- 
ble residue,  antimoniuretted  hydrogen  will  be  evolved,  to- 
gether with  free  hydrogen,  and  characteristic  smoky-  Tegt 
black  spots  or  stains  of  metallic  antimony  will  be  for 
deposited  from  it  upon  the  cold  porcelain.  To  be  Sb- 
sure  that  the  spots  are  really  composed  of  antimony  and  not 
of  arsenic,  cover  them  with  a  solution  of  bleaching  powder 
(Irypochlorite  of  calcium)  ;  if  they  are  antimony  spots  they 
will  not  dissolve,  while  arsenic  spots  dissolve  at  once.  (Com- 
pare Eliot  and  Storer's  Manual,  pp.  270,  271.) 

In  order  not  to  explode  the  test-tube  on  lighting  the  gas, 
the  operator  must  wait  patiently  for  several  minutes,  until 
all  the  air  has  been  expelled  from  the  tube. 

The  whole  of  the  antimony  is  not  converted  by  this  means 
into  antimoniuretted  hydrogen ;  a  portion  is  reduced  to  the 
metallic  state,  and  if  the  evolution  has  not  been  too  rapid, 
will  be  found  deposited  on  the  platinum  foil  as  a  firmly  adher- 
ent dark  coating  or  stain.  Therefore  when  the  zinc  in  the 
test-tube  is  all  or  nearly  all  consumed,  transfer  the  contents 
of  the  tube  to  a  porcelain  dish  and  examine  the  platinum 
foil  for  this  indication  of  the  presence  of  antimony. 

In  the  operation  just  performed,  the  tin  which  existed  as 
oxide  has  been  converted  into  the  metallic  state,  and  now 
awaits  examination  in  the  porcelain  dish.  Remove  and  rinse 
any  zinc  remaining  undissolved  and  carefully  decant  from  the 
dark  spongy  mass  in  the  dish,  the  solution  with  which  it  is 


34 


SEPARATION  OF  TIN. 


§  26 


covered  and  which  consists  mainly  of  chloride  of  zinc.     The 

residue  is  warmed  with  strong  chlorhydric  acid,  in  which  the 

tin  dissolves.     Pour  off  the   solution  of  protochloride  of  tin 

Test      thus  obtained,  and  add  to  it  two  or  three  drops  of 

for       a  solution  of  mercuric  chloride  (corrosive  sublimate) 

Sn«      (App.,  §  54).     A  white  or  gray  precipitate  of  mer- 

curous  chloride  (calomel),  often  mixed  with  gray  metallic 

mercury  will  be  thrown  down,  for :  — 

2HgCl2+SnCl2=2HgCl+SnCl4 ;  and 
2Hg01-f-SnCls=2Hg+SnCl4 . 

To  prove  that  the  precipitate  really  contains  calomel,  de- 
cant the  supernatant  liquid,  cover  the  precipitate  with  ammo- 
nia-water, and  heat  the  mixture  to  boiling  (compare  p.  18). 

26.  An  outline  of  the  foregoing  operations  may  be  repre- 
sented in  tabular  form  as  follows  :  — 


The  General  Reagent  (HSS)  of  Class  III  precipitates  As2S3 
Sb2S3,  and  SnS  or  SnSj,  [Au2S3  and  [PtS2].  (As  well  as  the 
members  of  Class  II,  from  which  Class  III  is  separated  by  solution 
in  sulphydrate  of  sodium.)  The  sulphydrate  of  sodium  solution  is 
treated  with  nitric  acid  and  nitrate  of  sodium,  and  the  mixture 
evaporated  and  heated  to  fusion.  The  fused  mass  is  treated  with 
cold  water :  — 


Arseniate  of  sodium 
(with  nitrate  of  so- 
dium, etc.)  goes 
solution.  Confirm  pres- 
ence of  As  by  magne- 
ium  mixture  and  by  the 
silver  test. 


Antimoniate  of  sodium  and  oxide  of  tin 
remain  undissolved.     Reduce    with    zinc 
into  and  HC1  in  presence  of  platinum  foil. 


Antimoniuretted  hy- 
drogen is  formed  and 
antimony  spots  ob- 
tained. 


Tin  is  left  in  the 
metallic  state  (to- 
gether with  some  an- 
timony which  stains 
the  foil).  Dissolve 
the  tin  in  HC1  and 
test  with  HgCl2 . 


In  the  case  of  mixtures  containing  gold  and  platinum  (see 
§  13),  as  well  as  arsenic,  antipony  and  tin,  the  gold  and 
platinum  would  remain  with  the  tin,  without  interfering  in  any 
way  with  the  separation  or  detection  of  either  member  of  the 


§  27         SEPARATION  OF  CLASSES  II  AND  111.  35 

class,  and  when  the  tin  reduced  by  zinc  is  dissolved  in  chlor- 
hydric  acid,  the  gold  and  platinum  would  remain  undissolved 
(together  with  some  antimony,  if  present).  Since  the  sul- 
phides of  gold  and  platinum  are  both  black,  while  those  of 
arsenic  and  tin  are  yellow  or  brown,  and  that  of  antimony  is 
orange,  the  presence  of  any  considerable  quantity  of  either 
of  the  precious  metals  would  be  indicated  by  the  black  color 
of  the  class  precipitate. 

There  are  excellent  special  tests  both  for  gold  and  for  plat- 
inum, by  which  these  elements  may  be  detected  even  in  the 
presence  of  all  the  other  metals.  Hence  it  is  most  conven- 
ient to  make  special  search  for  them  in  the  original  substance, 
by  methods  to  be  described  hereafter  (§  96,  b.),  whenever  the 
preliminary  examination  has  given  reason  to  suspect  the 
presence  of  either  of  them. 

27.  The  method  of  separating  Class  II  from  Class  III 
has  been  sufficiently  described  in  §§  8,  24.  When  members 
of  Class  II  are  altogether  absent,  something  may  be  learned 
from  the  color  of  the  precipitate  produced  by  sulphuretted 
hydrogen.  Thus,  — 

An  orange  colored  precipitate  indicates  the  presence  of 
antimony ; 

A  bright  yellow  precipitate,  the  presence  of  arsenic  ; 

A  dull  yellow  precipitate,  white  at  first,  the  presence  of 
bisulphide  of  tin  ; 

A  dark  brown  precipitate,  the  presence  of  protosulphide  of 
tin ; 

A  black  precipitate  the  presence  of  gold  or  platinum. 

When,  as  a  result  of  the  preliminary  examination  (§  80, 
III,  c),  there  is  reason  to  suspect  the  presence  of  mercury 
as  a  mercuric  salt,  sulphydrate  of  ammonium  which  has  be- 
come somewhat  yellow  from  standing,  should  be  substituted 
for  sulphydrate  of  sodium,  because  sulphide  of  mercury  is 
rather  soluble  in  sulphydrate  of  sodium.  In  the  event  of  the 
analysis  of  an  unknown  solution,  if  on  the  treatment  with' 
nitric  acid  of  the  solution  of  sulphides  in  sulphydrate  of  so- 


36  SEPARATION  OF  CLASSES  II  AND  III.          §  27 

dium,  a  black  precipitate  appear,  it  may  be  owing  to  the  pres- 
ence of  sulphide  of  mercury  and  not  to  gold  and  platinum  ;  it 
is  therefore  sometimes  better  in  such  a  case  to  dilute  the  solu- 
tion with  water,  filter  and  treat  the  precipitate  with  sulphydrate 
of  ammonium.  The  precipitate  remaining  undissolved  is 
added  to  the  regularly  obtained  precipitate  of  Class  II,  and 
the  sulphydrate  of  ammonium  solution  added,  with  a  fresh 
portion  of  strong  acid,  to  the  nitric  acid  solution  already  ob- 
tained. 

If  an  abundant  supply  of  the  substance  under  examination 
be  at  hand,  it  will  often  be  better  to  start  with  a  fresh  portion 
and  make  the  separation  of  the  two  classes  with  sulphydrate 
of  ammonium. 

Sulphide  of  copper  is  also  somewhat  soluble  in  the  sulphy- 
drates  of  sodium  and  ammonium,  in  presence  of  the  sulphides 
of  Class  III ;  but  enough  of  this  sulphide  will  always  remain 
undissolved  to  ensure  the  detection  of  copper  in  Class  II. 

Since  sulphydrate  of  ammonium  often  fails  to  dissolve  sul- 
phide of  tin,  it  is  not,  in  general,  so  fit  a  solvent  for  the 
sulphides  of  Class  III  as  sulphydrate  of  sodium.  In  either 
case  it  is  desirable  to  use  no  more  of  the  alkaline  sulphj^drate 
than  is  necessary,  on  account  of  the  amount  of  sulphur  which 
it  will  be  necessary  to  oxidize  with  nitric  acid  and  nitrate  of 
sodium. 


§  28  CLASS  IV.  37 


CHAPTER  V. 

CLASS  IV.  — ELEMENTS  WHOSE  HYDRATES  ARE  INSOLU- 
BLE IN  WATER,  AMMONIA- WATER  AND  SOLUTIONS 
OF  AMMONIUM  SALTS. 

28.  The  leading  fact  upon  which  the  separation  of  this 
class  is  based  is  the  insolubility  of  the  hydrates  of  iron,  alumi- 
num and  chromium  in  ammonia-water,  even  in  presence  of 
solutions  of  ammonium  salts.  But  these  three  hydrates  are 
not  the  only  substances  which  are  liable  to  be  precipitated  in 
an  actual  analysis  when  ammonia-water  is  added  in  excess  to 
a  solution  previously  acid.  There  are  a  number  of  com- 
pounds, soluble  in  acids,  but  not  in  water  or  in  weak  alkaline 
liquids,  which  are  thrown  down  without  change  when  their 
acid  solvent  is  destroyed. 

It  is  clear  that  it  is  needless  to  provide  in  this  place  against 
the  presence  of  such  salts  of  elements  belonging  to  Classes  I, 
II  and  III.  Those  elements  are  already  eliminated  when  the 
fourth  class  is  taken  in  hand.  But  if  there  are  any  salts  of 
elements  belonging  to  the  fourth  and  higher  classes  which  can 
only  be  kept  in  solution  by  a  free  acid,  they  will  be  precipi- 
tated without  change  in  consequence  of  the  neutralization  of 
their  solvent  by  the  ammonia-water  added  to  precipitate  the 
three  hydrates  above  mentioned.  Such  salts  are  the  phos- 
phates of  several  members  of  Classes  IV,  VI  and  VII,  besides 
a  number  of  oxalates,  borates,  silicates  and  fluorides  which 
occur  so  seldom  that  they  need  not  be  particularly  considered 
in  an  elementary  treatise.  Beside  the  phosphates,  several  chro- 
mites  and  aluminates  of  members  of  Classes  VI  and  VII  are 
insoluble  in  ammonia-water,  and  are  often  thrown  down  wholly 
or  in  part  along  with  the  legitimate  members  of  Class  IV. 
Manganese  also  (a  member  of  Class  V)  is  frequently  precipi- 


38  PRECIPITATION  OF  CLASS  IV.       §§  29,  30 

tated  in  combination  with  members  of  Class  IV,  in  the  form 
of  chromite,  ferrite  or  aluminate  of  manganese.  The  general 
scheme  for  the  examination  of  Class  IV,  necessarily  provides 
for  the  detection  of  all  the  members  of  the  class  in  the  pos- 
sible presence  of  these  extraneous  substances. 

29.  Example  of  the   Precipitation  with  Ammonia- 
water.  —  Pour  into  a  beaker  a  small  teaspoonful  of  aqueous 
solutions  (App.,  §  62)  of  sulphate  of  manganese,  common 
alum  (sulphate  of  aluminum   and   ammonium),  chrome  alum 
(sulphate  of  chromium  and  potassium),  and  chloride  of  iron 
(ferrous  chloride).     As  an  example  of  the  substances  insolu- 
ble in  water  which  might  be  present  in  an  acid  solution,  dis- 
solve  in   a   small   amount   of    boiling    chlorhydric    acid,   a 
not  very  large   quantity,   say  half  a  gramme,  of  bone-ash 
(phosphate  of  calcium),  and  add  the  solution  to  those  al- 
ready placed  in  the  beaker.     Fill  the  beaker  about  one  third 
full  of  water,  heat  the  mixture  to  boiling  and  add  to  it  two  or 
three  drops  of  strong  nitric  acid  to  convert  the  iron  into 
ferric  salts.     Boil  the  mixture  for  a  minute  or  two  and  then 
add,  little  by  little,  ammonia-water  to  the  boiling  liquor  until 
a  distinct  odor  of  ammonia  is  perceptible  after  the  mixture 
has  been  thoroughly  stirred. 

30.  Analysis  of  the  Mixed  Precipitate.— The  follow- 
ing method  of  detecting   iron,  chromium,    aluminum    (and 
manganese)  in  the  mixed  precipitate  which  may  contain  all 
of  them,  together  with  phosphates  and  other  compounds  of 
barium,  strontium,  calcium  and  magnesium,  depends:  —  1st. 
Upon  the  oxidation  and  conversion  of  the  hydrates  of  man- 
ganese and  chromium  into  manganate  and  chromate  of  sodium 
(or  potassium)  when  fused  with  a  mixture  of  carbonate  of 
sodium  and  nitrate  of  potassium  ;  while  the  hydrate  of  alum- 
inum under  the  same  treatment  is  converted,  to  a  greater  or 
less  extent,  into  aluminate  of  sodium,  and  the  compounds  of 
barium,  strontium  and  calcium  either  remain  unchanged  or  are 
converted  into  carbonates.     2d.  Upon  the  solubility  of  the 
chromate  and  aluminate  of  sodium  (or  potassium)  in  water 


§  30  SEPARATION  OF  CLASS  IV.  39 

and  the  insolubility  of  the  carbonates  or  other  compounds  of 
barium,  strontium  and  calcium  which  may  be  present  in  the 
fused  mass.  3d.  Upon  the  sparing  solubility  of  chromate 
of  lead  in  acetic  acid.  4th.  Upon  the  peculiar  green  color 
of  the  manganate  of  sodium  (or  potassium).  5th.  Upon  the 
fact  that  Prussian  blue  is  formed  when  a  solution  of  ferro- 
cyanide  of  potassium  is  added  to  the  solution  of  a  ferric  salt. 
6th.  Upon  the  sparing  solubility  of  the  oxalates  of  barium, 
strontium  and  calcium  in  dilute  acetic  acid. 

The  details  of  the  treatment  of  the  precipitate  produced 
by  ammonia-water,  are  as  follows :  —  Collect  the  precipitate 
upon  a  filter,  wash  it  two  or  three  times  with  water,  and  then 
dry  it  either  on  the  filter  or  by  transferring  it  to  a  piece  of 
platinum  foil  or  to  a  platinum  crucible  (App.,  §  80)  and  heat- 
ing over  the  lamp  gently  so  as  to  avoid  spattering.  The  dry 
precipitate  is  mixed  intimately  (best  by  rubbing  in  a  mor- 
tar) with  five  or  six  times  its  bulk  of  a  dry  mixture  of  equal 
parts  of  carbonate  of  sodium  and  nitrate  of  potassium  (App., 
§  36).  The  mixture  is  then  fused  thoroughly  by  heating  it 
over  the  lamp  either  on  platinum  foil  or  in  a  platinum  cruci- 
ble. If  the  amount  of  the  mixture  be  small,  a  piece  of  foil 
answers  very  well ;  larger  quantities  may  be  fused  in  succes- 
sive portions  on  the  foil,  but  a  small  crucible  is  much  more 
convenient. 

If  only  a  manganese  compound  and  no  chromium  had  been 
fused  on  the  foil,  the  cold  mass  would  have  exhibited  the 
peculiar  bluish-green  color  of  manganate  of  sodium  (or  po- 
tassium) 'owing  to  the  oxidation  of  a  small  portion  of  the 
hydrate  of  manganese  to  manganic  acid  in  the  presence  of 
carbonate  of  sodium  and  nitrate  of  potassium.  If  only  chro- 
mium had  been  present,  the  bright  yellow  color  of  chromate 
of  sodium  (or  potassium)  would  have  been  clearly  perceived. 
But  from  mixtures  of  the  manganate  and  chromate  of  sodium, 
(or  potassium)  in  various  proportions,  different  shades  of 
green,  brownish-green  or  yellowish-green,  will  result.  When 
iron  is  present,  the  red  color  of  its  oxide  may  obscure  the 
colors  due  to  manganese  and  chromium. 


40  SEPARATION  OF  CHROMIUM.  §  3Q 

Place  the  platinum  foil  or  crucible  in  a  porcelain  dish,  cover 
it  with  water,  and  boil  the  latter  until  all  the  soluble  matter 
has  been  dissolved  from  the  foil.  Take  out  the  foil,  rinse  it, 
and  throw  the  contents  of  the  dish  upon  a  filter.  The  man- 
ganate,  chromate  and  aluminate  of  sodium  pass  into  the  fil- 
trate, along  with  the  excess  of  the  carbonate  of  sodium  and 
nitrate  of  potassium  employed :  the  filtrate  is  colored  yel- 
low by  the  chromate.  The  insoluble  residue,  in  this  case, 
consists  of  the  oxides  of  iron  and  manganese,  together  with 
the  phosphate  of  calcium  which  has  not  been  altered  by  the 
fusion,  and  any  small  portion  of  carbonate  of  calcium  which 
may  have  been  formed  by  the  decomposition  of  a  part  of  the 
phosphate.  In  the  case  of  an  actual  analysis  there  might  be 
also  phosphates,  carbonates  and  other  insoluble  compounds 
of  barium,  strontium  and  magnesium. 

Divide  the  filtrate  from  the  insoluble  residue  of  the  fusion 
into  two  portions.     Carefully  add  acetic  acid,  drop  by  drop, 
to  one  of  these  portions  until  the  liquor  exhibits  an  acid  re- 
action, and  then  add  to  it  two  or  three  drops  of  a  solution  of 
acetate  of  lead  (App.,  §  45).     An  insoluble  precipitate  of 
chromate  of  lead  will  be  immediately  thrown  down,  exhibiting 
a  bright  yellow  color  if  the  reagents  be  all  pure.     But  if,  as 
often  happens,  the  carbonate  of  sodium,  employed  as  the 
Test      flux,  is  contaminated  with  sulphate  of  sodium,  the 
for       yellow  color  of  the  precipitate  will  tend  towards 
Cr.      white,  in  proportion  to  the  amount  of  sulphate  of 
lead  which  has 'gone  down  together  with  the  chromate.     A 
pure  white  precipitate  would  be  no  indication  of  chromium, 
but  only  of  a  sulphate  in  the  reagents. 

Acidulate  the  other  portion  of  the  aqueous  solution  of  the 
fused  sodium  (and  potassium)  compounds  with  dilute  chlor- 
Test      hydric  acid,  add  ammonia-water  to  slight  alkaline 
for       reaction,  warm  the  mixture  and  leave  it  at  rest  for 
Al.      at  least  half  an  hour  or,  better,  over  night.     After 
the  lapse  of  some  time,  a  characteristic,  gelatinous,  colorless 
agglomeration  of  particles  of  hydrate  of  aluminum  will  ap- 
pear at  the  top  or  bottom  of  the  liquid. 


§  30  SEPARATION  OF  ALUMINUM.  41 

It  should  be  said,  that  flocks  of  hydrate  of  aluminum,  when 
diffused  through  a  liquid,  are  almost  transparent  enough  to 
elude  observation.  When  an  acid  solution,  containing  much 
aluminum,  is  mixed  with  ammonia-water  and  warmed,  a 
copious  precipitate  of  hydrate  of  aluminum  will  appear  im- 
mediately, and  will  often  remain  floating  for  some  time  upon 
the  surface  of  the  solution  by  virtue  of  bubbles  of  air  en- 
tangled in  it.  But  since  it  is  not  easy  to  convert  the  whole 
of  the  alumina  in  the  original  precipitate  into  soluble  alumi- 
nate  of  sodium,  by  fusion  with  carbonate  of  sodium  in  the 
method  above  described,  the  quantity  of  the  hydrate  to  be 
thrown  down  at  the  final  test  is  often  very  small,  and  con- 
siderable time  must  be  allowed,  in  order  that  every  particle 
of  it  may  separate  from  the  solution,  and  all  the  particles 
collect  into  a  single  mass. 

To  confirm  the  presence  of  aluminum,  collect  the  hydrate 
in  the  point  of  a  small  filter  and  allow  it  to  drain.  Cut  away 
the  superfluous  paper,  place  that  portion  of  the  filter  to  which 
the  precipitate  is  attached  upon  a  piece  of  charcoal,  and  heat 
it  intensely  in  the  blowpipe  flame.  Moisten  the  residue  with 
a  drop  of  a  solution  of  nitrate  of  cobalt  and  again  ignite  it 
strongly.  The  unfused  compound  of  aluminum,  cobalt  and 
oxygen  left  upon  the  coal  will  exhibit  a  deep  sky-blue  color 
when  allowed  to  cool.  This  reaction  is  useful  in  distinguish- 
ing the  hydrate  of  aluminum  from  that  of  glucinum,  an 
element  somewhat  similar  to  aluminum  though  far  less 
abundant.  Hydrate  of  glucinum  when  ignited  with  nitrate 
of  cobalt  does  not  yield  a  pure  blue  compound,  but  only  a 
gray  mass. 

Return  now  to  the  insoluble  residue  of  the  fusion  with 
carbonate  of  sodium  and  nitrate  of^potassium.  If  the  char- 
acteristic color  of  the  manganate  of  sodium  (or  potassium) 
were  not  distinctly  observed  at  the  previous  fusion,  take 
a  small  quantit}?"  of  the  insoluble  residue  and  fuse  it  with 
twice  its  bulk  of  a  mixture  of  carbonate  of  sodium  and 
nitrate  of  potassium  upon  platinum  foil  in  a  strong  oxidizing 


42          SEPARATION  OF  MANGANESE  AND  IEON.      §  3Q 

blowpipe  flame   (App.,  §   78).       The  peculiar  bluish-green 
Test      coloration  of  manganate  of  sodium  will  appear  in 
for       the  fused  mass,  as  soon  as  it  has  become  cold,  par- 
Mru     ticulaiiy  at  the  edges  and  thinner  portions.     In  thus 
testing  for  manganese,  it  is  well  to  incline  the  foil,  so  that  por- 
tions of  the  thoroughly  melted  mass  may  flow  away  from  the 
centre  of  the  mixture  into  thin  sheets,  in  order  that  the  color 
of  the  manganate  may  be  exhibited  in  its  purity. 

Boil  a  second  small  portion  of  the  insoluble  residue  with  a 

little  strong  chlorhydric  acid,  dilute  the  solution  with  water, 

and  add  a  drop  or  two  of  ferrocyanide  of  potassium.     The 

liquid  will  immediately  become  colored  with  Prussian  blue, 

Test      an  indication  of  the  presence  of  iron.     In  case  much 

for       iron  be  present,  the  blue  color  may  be  too  deep  to 

•^e'      be  recognized  until  the  liquid  has  been  diluted  with 

a  large  quantity  of  water. 

Warm  another  portion  of  the  insoluble  residue  with  a  few 
drops  of  acetic  acid,  dilute  the  solution  with  water  and  filter 
if  anything  remain  undissolved.  To  the  slightly  acid  liquid 
add  a  teaspoonful  of  a  solution  of  oxalate  of  ammonium 
(App.,  §  20).  Any  compounds  of  barium,  strontium  and 
calcium  which  may  have  been  present  in  the  residue  will  be 
deposited  as  oxalates,  as  the  oxalates  of  these  elements  are 
but  sparingly  soluble  in  acetic  acid.  In  the  present  case  there 
will  be  a  precipitate  of  oxalate  of  calcium.  Allow  the  mix- 
ture to  stand  for  some  time  and  finally  collect  the  precipitate 
•on  a  filter,  wash,  dry  and  preserve  for  future  examination  in 
connection  with  Class  VI. 

In  addition  to  the  elements  present  in  the  solution  which 
has  just  been  analyzed,  compounds  of  magnesium  are  also 
under  certain  circumstances  precipitated  with  the  hydrates 
of  Class  IV.  In  actual  practice,  therefore,  the  remainder  of 
the  insoluble  residue  is  examined  for  magnesium,  as  follows  :  — 
Heat  the  mixture  strongly  on  the  platinum-foil  so  as  to  ren- 
der the  oxides  of  aluminum  and  iron  as  insoluble  as  pos- 
sible, and  then  treat  with  dilute  chlorhydric  acid  and  warm 


§31 


SEPARATION  OF  CLASS  IV. 


43 


gently.  Without  regarding  the  matter  which  remains  undis- 
solved  add  to  the  mixture  (which  contains  in  solution,  along 
with  the  magnesium,  some  iron,  aluminum,  calcium,  etc  )  a 
teaspoonful  of  chloride  of  ammonium,  and  ammonia- water  to 
alkaline  reaction.  Throw  the  mixture  upon  a  filter,  collect 
the  filtrate,  and  add  it  to  that  originally  obtained  from  the 
precipitate  of  Class  IV :  this  mixed  filtrate  will  be  examined 
in  due  course  (Class  VII,  for  magnesium.  In  case  the  whole 
amount  of  the  residue  from  the  fusion  of  the  precipitate  of 
the  class  with  carbonate  of  sodium  and  nitrate  of  potassium, 
be  but  small,  it  is  well  to  filter  the  liquid  of  the  preced- 
ing paragraph  which  contains  the  precipitated  oxalates  of 
barium,  strontium  and  calcium,  to  evaporate  the  filtrate  to 
dry  ness  and  ignite  to  destroy  the  oxalic  and  acetic  acids. 
The  residue  is  subsequently  treated  with  chlorhydric  acid, 
chloride  of  ammonium  and  ammonia,  filtered  and  the  filtrate 
added  to  the  filtrate  from  the  original  Class  IV  precipitate. 

31.     An  outline  of  the  foregoing  operations  may  be  tabu- 
lated as  follows :  — 


The  General  Reagent  ([NH4]HO  mixed  with  TsTH4Cl)  of  Class 
[V  precipitates  the  hydrates  of  Fe,Cr  and  Al  together  with  Mn 
(as  a  chromite,  ferrite  or  aluminate),  and  various  phosphates  and 
other  compounds  of  Fe,  Cr,  Al,  Ba,  Sr,  Ca  and  Mg.    The  pre- 
cipitate is  dried  and  fused  with  Na2CO3  and  KNO3  ;  the  fused 
mass  is  treated  with  water  and  filtered  :  — 

Divide  the  filtrate  into  two 
portions  .^  — 

Divide  the  precipitate  into  four 
portions  :  — 

Yellow  color 
of  the  solution 
indicates    Cr. 
Confirm  Cr  by 
precipitation 
of  PbCrO4. 

Acidulate  with 
HC1  and  add 
(NH4)HO  :  - 

Colorless  floc- 
culent  precipi- 
tate proves 
presence  of 
Al. 

Test  for 
Mnby 
fusing 
with 

CO3and 
JLNO3. 

Test  for 
Fe  with 
ferro  cy- 
anide of 
potas- 
sium. 

Test  for 
Ca,  etc. 
by  pre- 
cipita- 
tion of 
the  oxa- 
lates 
from 
acetic 
acid  so- 
lution. 

Elimi- 
nate Mg 
by  dis- 
solving 
inHCl 
and  re- 
precipi- 
tating 
Class  IV 
with 
NH4 
HO 

44  FEEBOUS  AND  FEEEIC  SALTS.  §  31, 32 

In  the  actual  examination  of  an  unknown  substance,  the 
analysis  is  somewhat  simplified,  if  the  substance  be  a  solid 
soluble  in  water,  or  if  it  be  a  neutral  solution,  or  if  by  any 
other  means  we  know  that  the  phosphates,  oxalates,  etc.,  men- 
tioned above  are  absent.  The  treatment  in  such  a  case  may  be 
simplified  by  the  omission  of  those  operations  looking  to  the 
separation  of  calcium,  barium,  etc.,  from  the  residue  of  the 
fusion  with  carbonate  of  sodium  and  nitrate  of  potassium. 

To  determine  whether  the  iron  in  the  substance  subjected 
to  analysis  was  originally  in  the  state  of  a  ferric  or  a  ferrous 
salt,  test  a  small  quantity  of  the  original  solution  with  a  drop 
of  ferricyanide  of  potassium  (App.,  §  34).  The  formation 
of  Prussian  blue  proves  the  presence  of  a  ferrous  salt.  An- 
other small  portion  of  the  original  solution,  tested  with  a 
drop  of  a.  ferrocyanide  of  potassium,  would  yield  Prussian 
blue  in  case  the  solution  contained  a  ferric  salt.  In  applying 
either  of  these  tests,  the  blue  coloration,  indicative  of  iron, 
is  alone  to  be  looked  for ;  no  notice  need  be  taken  of  other 
colorations,  or  of  precipitates  formed  by  the  action  of  the 
ferri-  or  ferro-cyanide  upon  the  various  metallic  salts  which 
the  solution  may  contain.  The  possibility  that  a  ferrous  salt 
may  have  been  changed  into  a  ferric  during  the  process  of 
getting  the  original  substance,  if  a  solid,  into  solution,  must 
not  be  lost  sight  of. 

32.  Separation  of  Class  IV  from  Class  III.  The 
methods  of  eliminating  Classes  I,  II  and  III  from  mixtures 
which  contain  members  of  these  classes  as  well  as  of  Class 
IV,  have  already  been  described  in  §§  6  and  8. 

It  is  essential  to  the  success  of  the  operation  that  all  the 
sulphuretted  hydrogen  in  the  filtrate  from  Classes  II  and  III 
be  expelled,  for  sulphuretted  hydrogen  precipitates  all  the 
members  of  Classes  IV  and  V  from  alkaline  solutions,  and 
the  filtrate  now  in  question  is,  of  course,  made  alkaline  when 
ammonia-water  is  added  to  it.  The  conversion  of  the  iron 
into  a  ferric  salt  (by  means  of  nitric  acid)  is  necessary  be- 
cause ferrous  hydrate  is  somewhat  soluble  in  ammonium-salts, 


§  32  FEEEOUS  AND  FEEEIC  SALTS.  45 

and  could  not,  therefore,  be  precipitated  completely  by  am- 
monia-water in  the  acid  filtrate  from  Classes  II  and  III. 

No  matter  what  the  condition  of  the  iron  may  have  been  in 
the  original  solution,  it  is  reduced  to  the  state  of  ferrous  salts 
by  sulphuretted  hydrogen.  The  filtrate  from  the  precipitate 
produced  by  sulphuretted  hydrogen  (the  general  reagent  of 
Classes  II  and  III)  should,  therefore,  be  placed  in  a  porcelain 
dish,  and  boiled,  until  the  steam  from  it  ceases  to  blacken  lead 
paper.  After  the  sulphuretted  hydrogen  has  been  expelled, 
three  or  four  drops  of  strong  nitric  acid  must  be  added  to  the 
liquid,  and  the  mixture  boiled  for  a  moment  longer  to  convert 
the  iron  into  ferric  salts.  If  by  accident  the  student  should 
fail  to  convert  the  iron  entirely  to  the  state  of  a  ferric  salt, 
there  will  be  produced  a  greenish,  slimy  precipitate  of  ferrous 
hydrate  on  the  addition  of  the  ammonia-water.  Such  a  pre- 
cipitate must  not  be  confounded  with  the  green  hydrate  of 
chromium :  it  should  be  redissolved  in  nitric  acid  and  the  acid 
solution  boiled  anew  for  a  few  minutes  before  reprecipitating 
with  ammonia-water. 

When  all  the  iron  has  been  converted  in  the  state  of  a 
ferric  salt,  a  small  quantity  of  a  solution  of  chloride  of 
ammonium  is  added  to  the  boiling  liquid,  and  finally  am- 
monia-water, little  by  little,  with  constant  stirring,  until  a 
persistent  odor  of  ammonia  is  perceptible.  A  large  excess 
of  ammonia  must  be  carefully  avoided,  for  hydrate  of  alumi- 
num, being  somewhat  soluble  in  ammonia-water,  might  be 
kept  in  solution,  to  the  disturbance  of  the  analysis  of  Classes 
VI  and  VII. 

It  will  be  remembered  that  the  object  of  using  chloride  of 
ammonium  is  to  hold  in  solution  magnesium  (of  Class  VII) 
and  the  members  of  Class  V.  This  it  does  in  virtue  of  the 
fact  that  the  double  salts  formed  by  the  union  of  ammonium 
compounds  with  compounds  of  the  elements  in  question  are 
soluble  in  water  and  also  in  ammonia-water.  A  considerable 
quantity  of  the  ammonium  salt  will,  of  course,  be  formed  in 
any  event  by  the  action  of  the  ammonia-water  upon  the 


46  PRECIPITATE  OF  CLASS  IV.  §  32 

chlorhydric  acid  in  the  solution,  but  it  is  best  always  to  add 
a  further  portion  of  the  chloride  as  a  precautionary  measure. 

The  following  inferences  may  be  drawn  from  the  color  of 
the  precipitate  produced  by  ammonia-water :  — 

A  gelatinous,  white  precipitate  indicates  aluminum  or  some 
one  of  the  oxalates,  phosphates,  etc.,  mentioned  above. 

A  grayish-green  or  grayish-blue  precipitate  indicates  chro- 
mium. 

A  reddish-brown  precipitate  indicates  iron. 

If  no  precipitate  is  produced  by  the  ammonia-water,  all 
the  members  of  Class  IV  are  absent,  and  the  solution  may 
at  once  be  tested  with  sulphydrate  of  ammonium,  the  general 
reagent  of  Class  V. 

When  the  solution  contains  much  chromium,  a  small  por- 
tion of  this  element  is  apt  to  remain  dissolved  at  first  in  the 
excess  of  ammonia-water,  and  to  color  the  solution  pink  ;  but 
by  continuing  to  boil  the  solution,  the  color  may  be  made  to 
disappear,  and  the  whole  of  the  chromium  may  be  thrown 
down.  Care  must  be  taken  to  replace,  by  small  portions, 
the  water  driven  off  by  boiling,  lest  some  of  the  members  of 
Class  V  be  rendered  insoluble. 

It  is  to  be  observed  that  the  legitimate  members  of  Class 
IV  cannot  be  completely  precipitated  by  ammonia-water  from 
solutions  which  contain  non-volatile  organic  substances,  like 
albumin,  sugar,  starch,  and  so  forth,  or  organic  acids  (such 
as  tartaric,  citric,  oxalic,  or  even  in  some  cases  acetic  acid) 
which  form  soluble  double  salts  by  uniting  simultaneously 
with  the  ammonium  and  one  or  more  of  the  members  of  the 
class.  The  treatment  of  substances  containing  organic  mat- 
ter will  be  explained  hereafter.  (§  82.) 


§§33,34  CLASS  V.  47 


CHAPTER  VI. 

CLASS  V.  — ELEMENTS  WHOSE  SULPHIDES  ARE  INSOL- 
UBLE IN  WATER  AND  IN  SALINE  OR  ALKALINE  SO- 
LUTIONS. 

33.  Example  of  tlie  Precipitation  of  the  Members 
of  Class  V. — Place  in  a  small  glass  flask  a  half  teaspoonful 
of  aqueous  solutions  (App.,  §  62)  of  the  sulphates,  nitrates, 
or  chlorides  of  cobalt,  nickel,  manganese  and  zinc.     Add  to 
the  mixture  five  or  six  teaspoonfuls  of  a  solution  of  chloride 
of  ammonium,  as  much  water,  and  ammonia- water  to  alkaline 
reaction. 

Heat  the  mixture  to  boiling,  and  add  sulphydrate  of  am- 
monium to  the  boiling  solution,  drop  by  drop,  with  frequent 
agitation,  as  long  as  a  precipitate  continues  to  be  formed. 
(Compare  p.  12 .)  In  the  present  case  there  are  special  reasons 
why  the  precipitate  should  be  boiled  and  shaken,  in  order  to 
make  it  compact ;  for  the  sulphides  of  Class  V,  when  loose 
and  flocculent,  are  not  only  easily  acted  upon  by  the  air  and 
by  dilute  acids,  but  are  peculiarly  liable  to  pass  through  the 
pores  of  filter-paper,  and  yield  muddy  filtrates. 

At  the  best,  these  sulphides  oxidize  rapidly  when  moist, 
with  formation  of  soluble  sulphates  which  are  liable  to  pass 
through  the  filters  and  contaminate  the  filtrates.  The  analysis 
of  the  sulphides  should  therefore  be  proceeded  with  imme- 
diately after  the  precipitation  with  sulphydrate  of  ammonium, 
and  should  be  conducted  in  such  manner  that  no  precipitate 
of  a  sulphide  shall  ever  be  left  moist  upon  a  filter  more  than 
half  an  hour. 

34.  Analysis  of  the  Mixed  Sulphides. — The  detection 
of  the  several  members  of  Class  V  depends  :  —  1st.     Upon 
the  almost  complete  insolubility  of  the  sulphides  of  cobalt 


48         SEPARATION  OF  MANGANESE.        §  34 

and  nickel  in  cold  dilute  chlorhydric  acid ,  and  the  ready  solu- 
bility of  the  sulphides  of  manganese  and  zinc  in"  that  liquid. 
2d.  Upon  the  solubility  of  hydrate  of  zinc,  and  the  insolu- 
bility of  hydrate  of  manganese,  in  a  solution  of  caustic  soda. 
3d.  Upon  the  insolubility  of  sulphide  of  zinc  in  alkaline 
solutions.  4th.  Upon  the  peculiar  colors  imparted  to  borax 
glass  by  compounds  of  cobalt  and  nickel  dissolved  in  the 
glass ;  and  upon  certain  other  special  tests  to  be  described 
directly. 

To  effect  the  separation :  —  Collect  the  precipitate  upon  a 
filter,  and  rinse  it  once  or  twice  with  water ;  spread  open  the 
filter  in  a  porcelain  dish,  and  cover  it  with  cold  dilute  chlor- 
hydric acid.  Scarcely  any  of  the  sulphide  of  cobalt,  or  of 
nickel,  will  go  into  solution,  while  the  sulphides  of  manganese 
and  zinc  will  be  completely  decomposed,  and  dissolved  as 
chlorides. 

Filter  the  chlorhydric  acid  solution,  pour  the  filtrate  into  a 
porcelain  dish,  and  boil  it  until  strips  of  moistened  lead  paper 
held  in  the  steam  no  longer  indicate  the  presence  of  sulphur- 
etted hydrogen  ;  then  add  caustic  soda  to  the  liquid  in  slight 
excess.  A  whitish  gelatinous  precipitate  of  hydrate  of  man- 
ganese, insoluble  in  caustic  soda,  will  be  thrown  down,  to- 
gether with  small  portions  of  the  hydrates  of  cobalt  and 
nickel,  resulting  from  the  partial  decomposition  of  the  sul- 
phides of  these  metals  by  the  chlorhydric  acid,  while  the 
hydrate  of  zinc  at  first  precipitated  redissolves  completely  in 
the  excess  of  soda.  It  is  to  be  observed  that  precipitation 
should  never  be  effected  in  a  porcelain  dish,  since  a  white  or 
transparent  precipitate  is  scarcely  visible  in  a  white  and 
opaque  dish. 

To  prove  the  presence  of  manganese,  collect  the  precipitate 
upon  a  filter,  allow  it  to  drain,  and  fuse  a  small  portion  of  it 

Test  with  a  mixture  of  carbonate  of  sodium  and  nitrate 
for  of  potassium  upon  platinum  foil  in  the  oxidizing 

•^n«      blowpipe  flame,  as  directed  on  p.  4^. 

Through  the  alkaline  filtrate  pass  sulphuretted  hydrogen 


§  34  SEPAEATION  OF  ZINC.  49 

gas.     Sulphide  of  zinc  will  be  thrown  down  as  white  or  dirty- 
white  flocculent  precipitate. 

To  confirm  the  presence  of  zinc  :  —  Collect  the  precipitate 
produced  by  sulphuretted  hydrogen  upon  a  filter  and  allow  to 
drain ;  transfer  it  to  a  porcelain  dish,  dissolve  it  in  dilute 
chlorhydric  acid,  and  evaporate  the  solution  almost  to  dryness 
on  a  water-bath  (App.,  §  77).     Dissolve  the  residue  in  a  few 
drops  of  water,  and  without  heeding  the  inilkiness  which  the 
presence  of  particles  of  free  sulphur  may  produce  in  it,  pour 
this  liquid  into  a  test-tube  containing  two  or  three  teaspoon- 
fuls  of  a  solution  of  normal  chromate  of  potassium  previously 
heated  to   boiling.     A  peculiar,  yellow,  somewhat      Test 
flocculent  precipitate  of  basic  chromate  of  zinc  will       for 
form  in  the  boiling  liquid,  and  will  soon  subside  to      Zn« 
the  bottom  of  the  tube.     The  red  color  of  the  supernatant 
fluid  is  due  to  the  formation  of  bichromate  of  potassium. 

It  is  to  be  observed  that  in  the  analysis  of  mixtures  which 
contain  no  manganese,  the  precipitate  of  hydrate  of  cobalt  or 
of  nickel,  produced  by  the  caustic  soda,  is  usually  small  and 
sometimes  hardly  perceptible  ;  but,  no  matter  how  minute  the 
precipitate  may  be,  it  must  always  be  carefully  removed  by 
filtration  before  testing  the  solution  for  zinc  with  sulphuretted 
hydrogen. 

The  black  residue,  insoluble  in  dilute  chlorhydric  acid,  is 
washed  with  water  and  tested  for  cobalt  and  nickel,  by  heat- 
ing successive  small  portions  of  it  in  a  bead  (§  89,  c.)     Tests 
of  borax  (App.,  §  25)  in  the  oxidizing  blowpipe       for 
flame.     If  cobalt  alone  were  present,  a  bright,  pure  Co&Ni. 
blue  color  would  be  imparted  to  the  bead.     On  the  other  hand, 
if  the  precipitate  was  composed  solely  of  sulphide  of  nickel, 
the  borax  glass  would  assume  a  peculiar  reddish-brown  color. 
Mixtures  of  the  two  sulphides  yield  beads  of  various  tints, 
according  to  the  proportions  of  nickel  and  cobalt  contained 
in  them.     By  adding  the  precipitate  to  the  borax  by  repeated 
small  portions,  and  fusing  the  bead  anew  after  each  addition, 

it  is  often  possible  to  obtain  first  the  characteristic  color  of 

5 


50  SEPARATION  OF  NICKEL.  §  34 

one  of  the  elements,  and  afterwards  tolerably  well  defined 
indications  of  the  other. 

The  blue  color  of  cobalt  can  usually  be  made  manifest, 
even  in  presence  of  much  nickel,  by  heating  the  borax  bead 
in  the  reducing  blowpipe  flame  (App.,  §  78).  In  the  reduc- 
ing flame  the  reddish-brown  color  imparted  by  nickel  changes 
to  gray,  while  the  cobalt  blue  remains  unaltered. 

In  any  event,  one  of  the  two  metals  will  be  detected  by 
the  blowpipe  test,  and  the  subsequent  operations  can  be 
limited  to  searching  for  the  other. 

To  prove  the  presence  of  nickel,  boil  the  black  residue  with 
a  few  drops  of  aqua  regia  in  the  porcelain  dish,  and  evaporate 
the  solution  almost,  but  not  quite,  to  dryness.  Add  to  the 
residual  acid  liquor,  little  by  little,  a  strong  solution  of 
cyanide  of  potassium,  until  the  reaction  of  the  solution  be- 
comes decidedly  akaline,  and  boil  the  mixture  for  five  min- 
utes, taking  care  to  add  water  by  small  portions  to  fully 
replace  that  lost  by  evaporation.  The  cyanides  of  nickel 
and  cobalt,  at  first  thrown  down,  both  redissolve  easily  in  an 
excess  of  cyanide  of  potassium,  but  while  the  cyanide  of 
nickel  undergoes  no  change  when  the  mixture  is  boiled,  the 
cyanide  of  cobalt  is  all  converted  into  cobalticyanide  of 
potassium,  and  from  solutions  of  this  compound,  cyanide  of 
cobalt  is  not  precipitated  on  the  addition  of  acids. 

As  soon  as  the  liquid  has  become  cold,  pour  dilute  sul- 
phuric acid  into  it,  without  heeding  any  precipitate  which 
may  have  formed  during  the  evaporation,  until  a  drop  of  the 
mixture  turns  blue  litmus  paper  red.  Transfer  the  acidulated 

Test  liquor  to  a  large  test-tube,  fill  the  latter  with  water, 
for  shake  the  mixture  well,  and  allow  it  to  stand  during 

^Ni-  eighteen  or  twenty-four  hours.  The  soluble  com- 
pound of  cyanide  of  nickel  and  cyanide  of  potassium  is 
decomposed  by  the  sulphuric  acid,  and  the  cyanide  of  nickel 
precipitated  in  the  form  of  a  light,  dirty  greenish-yellow 
powder,  which  slowly  subsides  to  the  bottom  of  the  tube. 

Sometimes  a  dark  layer  of  dirt,  derived  from  impurities  in 


§§  34,  35     SEPARATION  OF  COBALT.  51 

the  reagents,  is  deposited  above  or  below  the  stratum  of 
cyanide  of  nickel,  but  it  seldom  happens  that  the  character- 
istic color  of  the  latter  is  materially  obscured  by  this  con- 
tamination. At  other  times,  when  the  operations  have  been 
performed  carelessly,  and  the  reagents  have  been  employed 
in  undue  quantities,  crystals  of  sulphate  of  potassium  will 
separate  in  the  tube ;  but  they  can  readily  be  removed  by 
dissolving  them  in  water. 

To  confirm  the  presence  of  cobalt  in  case  of  doubt : — dissolve 
the  black  residue  in  a  few  drops  of  hot  aqua  regia,  evaporate 
the  solution  nearly  to  dryness,  pour  into  the  residual  solution 
two  or  three  times  its  own  volume  of  a  solution  of  nitrite  of 
potassium  (App.,  §  37),  and  add  to  the  mixture  concentrated 
acetic  acid,  until  the  reaction  of  the  liquid  is  strongly  acid. 
Transfer  the  mixture  to  a  test-tube,  and  leave  it  at  -    Test 
rest  during  eighteen  or  twenty-four  hours.     A  beau-      for 
tiful,  yellow  crystalline  precipitate  of  the  double      Co' 
nitrite  of  cobalt  and  potassium  will  be  deposited  sooner  or 
later,  according  to  the  proportion  of  cobalt  which  the  solution 
contained. 

On  adding  caustic  soda  to  the  filtrate  from  the  cobalt 
precipitate,  hydrate  of  nickel  would  be  thrown  down  if  pres- 
ent, and  the  presence  of  nickel  might  be  confirmed  by  testing 
this  precipitate  with  borax  in  the  oxidizing  blowpipe  flame. 

35.  An  outline  of  the  foregoing  operations  may  be  tabu- 
lated as  follows :  — 


The  General  Reagent  ([NHJHS)  of  Class  V  precipitates  CoS, 
NiS,  MnS  and  ZnS.    Treat  the  precipitate  with  dilute  HC  1  :  — 

CoS  and  WiS 
remain  undis- 
solved. 
Test  for  Co 
and   Ni  with 
borax       glass 
and,    if    need 
be,  with  KCN 
orKNO2. 

MnCl2  and  ZnClgo  into  solution.      Boil,  to  ex- 
pel H2S,  and  add  NaHO  :  — 

Hydrate  of  manganese  is 
precipitated,  together  with 
traces  of  the  hydrates  of 
Co  and  Ni. 
Prove  presence  of  Mn  by 
the  blowpipe  test. 

Hydrate  of  zinc  goes 
into  solution.  Add  H  ,S 
to  tnrow  down  ZnS. 
Confirm  presence  of 
Zn  by  precipitation  of 
the  chromate. 

52  SEPARATION  OF  CLASSES  IV  AND   V.  §  36 

36,  Separation  of  Class  V  from  Class  IV.  —  After 
Classes  I,  II,  III  and  IV  have  been  removed  in  the  manner 
already  described  (§§  9,  32),  add  a  single  drop  of  sulphydrate 
of  ammonium  of  good  quality  (App.,  §  17)  to  the  filtrate 
from  Class  IV.  If  no  precipitate  is  produced,  none  of  the 
members  of  Class  V  can  be  present,  and  the  solution  may  be 
immediately  tested  with  carbonate  of  ammonium,  the  general 
reagent  of  Class  VI. 

If  the  first  drop  of  the  sulphydrate  produces  a  precipitate, 
transfer  the  mixture  to  a  small  flask,  heat  it  until  it  actually 
boils  and  add  more  of  the  sulphydrate,  with  the  precautions 
enjoined  on  p.  12  to  complete  the  precipitation.  / 

In  case  the  precipitate  produced  by  sulphydrate  of  am- 
monium is  white,  the  presence  of  zinc  is  indicated. 

If  it  be  flesh-colored,  or  yellowish-white,  and  becomes 
brown  by  oxidation  when  exposed  to  the  air,  the  presence  of 
manganese  is  to  be  inferred. 

In  case  the  precipitate  is  black,  either  cobalt  or  nickel,  or 
both  these  elements,  are  present.  Both  of  them  must  be 
sought  for,  whenever  the  precipitate  exhibits  any  tinge  of 
black  at  the  moment  of  its  formation. 


§§  37,  38  CLASS  VI.  53 


CHAPTER  VII. 

CLASS  VI. -ELEMENTS  WHOSE  CAKBONATES  ARE  INSOL- 
UBLE IN  WATEB,  AMMONIA-WATER  AND  SALINE  SOLU- 
TIONS. 

37.  Example  of  the  Precipitation  of  the  Members  of 
Class  VI.  —  Place  in  a  small  beaker  a  teaspoonful  of  aque- 
ous solutions  of  the  chlorides  or  nitrates  of  barium,  stron- 
tium  and  calcium.      Add    to    the   mixture    two    or    three 
teaspoonfuls  of  a  solution  of  chloride  of  ammonium,  enough 
ammonia-water  to  produce  an  alkaline  reaction,  and  finally  a 
solution  of  carbonate  of  ammonium,  drop  by  drop,  as  long 
as  any  precipitate  continues  to  be  produced  b}~  fresh  portions 
of  this  reagent.     To  determine  this  last  point,  heat  the  mix- 
ture to  boiling  at  intervals,  and  after  boiling  allow  it  to  settle, 
until  a  sufficient  quantity  of  comparatively  clear  liquid  has 
collected  at  the  top  of  the  mixture  to  permit  the  application 
of  the  test.- 

38.  Analysis  of  the  Mixed  Carbonates. — The  separa- 
tion of  barium,  strontium  and  calcium,  one  from  the  other, 
depends  :  —  1st.  Upon  the  insolubility  of  chromate  of  barium 
in  dilute  acetic  acid,  and  the  solubility  of  the  chromates  of 
strontium  and  calcium  in  that  liquid.     2d.  Upon  the  fact  that 
sulphate  of  strontium  is  almost  absolutely  insoluble  in  acidu- 
lated water,  while  sulphate  of  calcium,  though  rather  spar- 
ingly soluble  in  water,  is  still  sufficiently  soluble  to  be  kept 
in  solution.     (See  App.,  §  30.) 

Collect  the  precipitnte  upon  a  filter,  wash  it  two  or  three 
times  with  water,  taking  care  to  collect  the  precipitate  at  the 
apex  of  the  filter,  and  dissolve  it  in  acetic  acid.  The  acid 
may  be  poured  into  the  filter  as  it  rests  in  the  funnel,  but 


54  SEPARATION  OF  BAEIUM.  §  38 

only  a  few  drops  should  be  used,  and  the  filtrate  should  be 
poured  back  repeatedly  upon  the  filter,  until  all  the  precipi- 
tate has  been  dissolved.  If  the  portion  of  acid  at  first  taken 
becomes  saturated  before  the  precipitate  is  entirely  dissolved, 
it  will  be  necessary  to  add  an  additional  small  amount. 
Finally  rinse  the  filter  with  a  little  water  from  a  wash-bottle 
with  small  orifice,  collect  the  wash-water  with  the  filtrate, 
and  shake  the  mixture. 

Pour  a  small  portion  of  the  acetic  acid  solution  into  a  test- 
tube,  and  add  to  it  a  drop  of  a  solution  of  normal  chromate 
of  potassium.     A  pale  yellow  precipitate  falls  when  barium 
is  present,  as  in  this  instance  ;  for  chromate  of  barium  is  well- 
Test      ni»u  insoluble  in  acetic  acid,  especial!}'  in  presence 
for      of  saline  solutions.     In  order  to  separate  the  whole 
Ba"      of  the  barium,  pour  the  contents  of  the  test-tube 
into  the  reserved  portion  of  the  acetic  acid  solution,  heat  the 
mixture  to  boiling,  and  add  to  it  chromate  of  potassium,  until 
no  more  precipitate  falls  and  the  supernatant  liquor  appears 
distinctly  yellow,  after  having  been  well  shaken  and  allowed 
to  settle.     Filter  the  mixture,  and  proceed  to  examine  the 
filtrate  for  strontium  and  calcium. 

If  no  barium  had  been  present,  no  precipitate  would  have 
been  produced  by  chromate  of  potassium  in  the  small  portion 
of  liquid  first  tested,  and  it  would  have  been  unnecessary  to 
mix  this  reagent  with  the  rest  of  the  acetic  acid  solution. 
Trouble  would  thus  be  saved,  as  will  appear  below. 

It  sometimes  happens  that  chromate  of  barium  is  precipi- 
tated in  the  form  of  powder  so  fine  that  some  particles  of  it 
pass  through  the  pores  of  the  paper  and  contaminate  the  fil- 
trate. Now,  in  order  to  detect  strontium  and  calcium  it  is 
absolutely  necessary  that  this  filtrate,  although  of  a  bright 
yellow  color,  should  be  perfectly  transparent  and  free  from 
suspended  particles  of  the  barium  salt.  If  then  the  filtrate 
is  at  all  turbid,  it  must  be  poured  back  repeatedly  into  the 
filter,  and  again  collected  in  clean  tubes,  until  the  last  trace 
of  cloudiness  has  disappeared. 


§  38   SEPARATION  OF  STRONTIUM  AND  CALCIUM.      55 

To  the  filtrate  from  the  chromate  of  barium  add  ammonia- 
water  to  alkaline  reaction,  and  carbonate  of  ammonium  as 
long  as  a  precipitate  falls.  Heat  the  mixture  to  boiling  for  a 
moment,  collect  the  precipitate  upon  a  small  filter,  and  wash 
it  with  water,  until  all  the  chromate  of  potassium  has  been 
removed,  and  the  wash-water  runs  colorless  from  the  filter. 

Dissolve  the  precipitate  in  the  smallest  possible  quantity 
of  acetic  acid,  and  mix  it  with  three  or  four  times  its  volume 
of  a  solution  of  sulphate  of  potassium  (App.,  §  30),  made 
of  such  strength  that,  though  capable  of  throwing  down  sul- 
phate of  strontium,  it  cannot  precipitate  sulphate  of  calcium. 
Allow  the  mixture  to  stand  at  rest  for  two  hours  or  more,  in 
order  that  the  white  powder  of  sulphate  of  strontium     Testg 
may  separate  completely.     Then  filter,  and  to  the       for 
filtrate  add  ammonia-water  to  alkaline  reaction,  and  Sr&Ca. 
half  a  teaspoonful  of  a  solution  of  oxalate  of  ammonium. 
A  white  precipitate  of  oxalate  of  calcium  will  be  immediately 
thrown  down. 

Since  sulphate  of  strontium  is  somewhat  soluble  in  a  solu- 
tion of  chromate  of  potassium,  the  filtrate  from  chromate  of 
barium  cannot  be  examined  directly  for  strontium  by  means 
of  sulphate  of  potassium.  The  strontium  and  calcium  are 
consequently  reprecipitated  as  carbonates,  in  order  that  the 
excess  of  chromate  of  potassium  may  be  washed  away.  The 
operation  serves  also  to  collect  the  strontium  and  calcium  out 
of  the  mass  of  liquid  in  which  they  have  become  diffused,  and 
to  concentrate  them  to  a  small  bulk. 

It  should  be  observed  that,  when  the  proportion  of  stron- 
tium or  calcium  in  a  mixture  is  small,  it  often  happens  that 
the  precipitate,  produced  by  carbonate  of  ammonium  in  the 
filtrate  from  chromate  of  barium,  is  held  in  suspension  and 
concealed  so  completely  in  the  yellow  liquor,  that  an  unprac- 
tised eye  can  hardly  detect  the  fact  that  the  liquid  has  become 
cloudy.  That  a  precipitate  has  really  been  formed  in  such 
cases  is  easily  discovered  by  throwing  a  portion  of  the  mix- 
ture upon  a  filter,  and  comparing  the  clear  filtrate  thus  ob- 


56  SEPARATION  OF  CLASS  VI.          §§  39,  40 

tained  with  that  portion  of  the  mixture  which  has  been  left 
unfiltered. 

39.     An  outline  of  the  foregoing  operations  may  be  pre- 
sented in  tabular  form,  as  follows :  — 


The  General  Eeagent,  [!N"H4]2CO3,  of  Class  VI  precipitates  the 
carbonates  of  Ba,  Sr  and  Ca.  Dissolve  in  dilute  acetic  acid,  and 
addK2Cr04:- 


BaCrO4 

is   thrown 

down 

as  a 

yellow 

powder. 


Sr  and  Ca  remain  in  solution.  Add  (NH4)HO  and 
(NH4)2CO3.  Collect  and  wash  the  precipitate,  and  dis- 
solve it  in  acetic  acid.  Add  dilute  K2SO4 :  — 


SrSO4  is 

thrown 
down. 


Ca  remains  in  solution.  Add  oxalate  of 
ammonium,  to  precipitate  the  calcium  as 
oxalate. 


40.  Separation  of  Class  VI  from  the  Preceding 
Classes.  —  After  Classes  I,  II,  III,  IV  and  V  have  been  sepa- 
rated in  the  manner  already  described  (§§  6  to  10),  there  will 
still  always  remain  to  be  examined  the  nitrate  from  Class  V, 
and  sometimes  a  precipitate  (§  30)  composed  of  oxalates  of 
barium,  strontium,  calcium  (and  magnesium),  —  in  case  any 
salt  of  these  elements,  insoluble  in  ammonia-water,  has  been 
thrown  down  with  the  members  of  Class  IV. 

If  such  a  precipitate  has  been  obtained  in  the  analysis  of 
Class  IV,  the  oxalic  acid  contained  in  it  must  now  be  de- 
stroyed, the  remainder  of  the  precipitate  brought  into  solution, 
and  this  solution  added  to  the  nitrate  from  Class  V,  before 
proceeding  to  precipitate  the  members  of  Class  VI.  To  this 
end,  ignite  the  dry  precipitate  carefully  upon  platinum  foil, — 
by  several  successive  portions  if  the  precipitate  is  large,  — 
taking  care  that  none  of  the  powder  is  left  sticking  to  the 
paper  or  lost  by  dropping  it  from  the  foil.  At  a  moderate 
heat  the  oxalates  suffer  decomposition,  and  only  carbonates 
or  oxides  are  left  upon  the  foil.  Place  the  foil  and  the  residue 
in  a  small  porcelain  dish,  and  dissolve  the  residue  in  boiling 
dilute  chlorhydric  acid.  Add  a  few  drops  of  chloride  of  am- 


§  40  SEPARATION  OF  CLASS   VI.  57 

monium  to  the  solution,  neutralize  the  acid  with  ammonia- 
water,  pour  the  liquid  upon  a  small  filter  and  add  the  filtrate 
to  that  obtained  from  Class  V.  Then  add  a  solution  of  car- 
bonate of  ammonium  to  the  mixture,  and  boil  it  in  the  man- 
ner described  in  §  37. 

If  there  be  no  precipitate  of  the  oxalates  from  Class  IV, 
the  filtrate  from  Class  V  will,  of  course,  be  treated  directly 
with  carbonate  of  ammonium,  care  being  taken  to  add  only 
a  drop  or  two  of  the  reagent,  at  first,  to  ascertain  whether 
any  of  the  members  of  Class  VI  are  really  contained  in  the 
solution. 

The  solution  to  which  the  general  reagent  carbonate  of 
ammonium  is  added,  must  contain  chloride  of  ammonium,  to 
prevent  the  precipitation  of  magnesium  as  a  carbonate,  and 
also  ammonia-water,  to  hmder  the  decomposition  of  the  car- 
bonates of  barium,  strontium  and  calcium  by  the  boiling 
chloride  of  ammonium.  But  since  the  excess  of  ammonia- 
water  and  the  chloride  of  ammonium,  added  to  the  solution 
before  the. separation  of  Class  IV,  are  still  contained  in  it,  no 
new  quantity  of  either  of  them  need  here  be  added. 

It  is  to  be  remembered,  in  this  connection,  that  the  carbon- 
ates of  barium,  strontium  and  calcium  are  all  slightly  soluble 
in  a  solution  of  chloride  of  ammonium,  and  that  no  precipi- 
tate whatever  is  produced  when  carbonate  of  ammonium  is 
added  to  a  weak  solution  of  either  of  the  members  of  Class 
VI,  in  case  a  large  quantity  of  chloride  of  ammonium  has 
been  previously  mixed  with  it.  On  this  account  it  is  well  in 
an  actual  analysis  to  concentrate  by  evaporation  the  filtrate 
from  the  Class  V  precipitate  before  adding  the  carbonate  of 
ammonium  solution, 

In  a  solution  containing  traces  of  barium  or  strontium  these 
elements  might  fail  to  be  detected,  in  case  the  chlorhydric 
acid  employed  in  the  process  of  separating  Classes  I  and  II 
was  contaminated  with  sulphuric  acid,  or  in  case  the  original 
liquid  contained  nitric  acid  to  oxidize  a  portion  of  the  sul- 
phur of  the  sulphuretted  hydrogen  employed  to  precipitate 


58  SEPARATION"  OF  CLASS   VI.  §  40 

Class  II,  or  even  if  the  nitric  acid,  employed  to  oxidize  iron 
in  the  filtrate  from  Classes  II  and  III,  were  added  before  the 
sulphuretted  hydrogen  had  been  expelled.  All  danger  is 
avoided,  however,  by  using  pure  chlorhydric  acid  to  precipi- 
tate Class  I,  and  expelling  the  nitric  acid  from  the  filtrate  by 
evaporating  the  latter  to  dryness  upon  a  water-bath,  cover- 
ing the  residue  with  pure  concentrated  chlorhydric  acid,  again 
evaporating  until  the  mixture  becomes  dry,  and  finally  dis- 
solving in  water  acidulated  with  chlorhydric  acid. 


§§  41,42  CLASS  VII.  59 


CHAPTER  VIII. 

CLASS  VII.— INCLUDES  THE  REMAINING-  COMMON  ELE- 
MENTS NOT  COMPRISED  IN  THE  PRECEDING  CLASSES, 
NAMELY:  MAGNESIUM,  SODIUM  AND  POTASSIUM. 

41.  The  Detection  of  the  Several  Members  of  Class 
III  depends  :  —  1st.  Upon  the  insolubility  of  a  double  phos- 
phate of  magnesium  and  ammonium,  and  the  .solubility  of 
the  phosphates  of  potassium  and  of  sodium ;  and  2d.  Upon 
the  fact  that  compounds  of  sodium  and  potassium  impart 
peculiar  colorations  to  non-luminous  flames,  like  those  of 
alcohol  and  of  a  mixture  of  coal-gas  and  air. 

Prepare  a   mixture   of   a  small   teaspoonful  of  solutions 
(App.,  §  62)  of  almost  any  one  of  the  salts  of  magnesium, 
sodium  and  potassium,  and  add  to  the  mixture  an  equal  bulk 
of  chloride  of  ammonium.     Pour  a  quarter  of  the  mixture 
into  a  test-tube  and  the  remainder  into  a  small  porcelain  dish. 
Add  to  the  contents  of  the  test-tube  two  or  three  drops  of  a 
solution  of  phosphate  of  sodium,  and  as  much  ammonia- 
water,  and  shake  the  cold  mixture  at  frequent  inter-      Test 
vals  during  one  or  two  hours.     A  crystalline,  white       for 
precipitate  of  phosphate  of  magnesium  and  ammo-     '&&• 
nium  will  appear  after  a  longer  or  shorter  interval,  according 
as  the  original  solution  was  more  or  less  dilute. 

42.  Evaporate  the  contents  of  the  porcelain  dish  to  dry- 
ness,  ignite  the  residue  until  the  chloride  of  ammonium  has 
been  completely  expelled,  —  a  point  which  will  be  indicated 
by  the  cessation  of  fuming,  —  allow  the  dish  to  cool,  and 
pour  into  it  three  or  four  drops  of  water. 

Carefully  clean  the  loop  on  a  piece  of  platinum  wire  by 
washing  it  repeatedly  with  water,  and  finally  holding  .it  in 


60       SEPARATION'  OF  SODIUM  AND  POTASSIUM:.    §42 

the  lamp  flame  until  the  last  traces  of  sodium  compounds  are 
Test      burned  off,  and  it  ceases  to  color  the  flame.      With- 
for       out  touching  the  loop  with  the  fingers,  dip  it  into 
•^a'      the  aqueous  solution  in  the  dish,  and  again  hold  it 
in  the  flame.  A  bright  yellow  color  will  be  imparted  to  the  flame 
by  the  sodium  contained  in  the  mixture  ;  but  the  color  pecu- 
liar to  potassium  compounds  will  be  invisible,  since  the  yel- 
low  color  of  the  sodium  overpowers  and  conceals  it.     Dip  the 
loop  a  second  time  in  the  solution,  and  again  hold  it  in  the 
lamp  flame  ;  but  this  time  look  at  the  flame  through  a  piece 
of  deep-blue  cobalt  glass,.    This  cobalt  glass  is  the  ordinary 
blue  glass  used  for  stained  glass  windows  ;  it  is  essential  that 
the  glass  should  be  of  moderate  thickness,  and  colored  blue 
throughout,  not  simply  "flashed"  with  blue.     The  character- 
Test      istic  violet  color  imparted  to  a  flame  by  potassium 
for       compounds  will  now  be  visible,  for  the  blue  glass 
^»       shuts  off  completely  the  yellow  sodium  light,  while 
it  permits  the  free  passage  of  the  violet  rays. 

Since  traces  of  compounds  of  sodium  and  potassium  are 
to  be  found  almost  everywhere,  it  is  sometimes  difficult  to 
determine  by  the  foregoing  tests  whether  the  substance  under 
examination  contains  one  or  the  other  of  these  elements  as  an 
essential  ingredient,  or  merely  as  an  accidental  impurity. 
It  is  always  possible,  however,  to  separate  the  sodium  or  the 
potassium  from  the  other  members  of  the  class,  and  to  decide, 
by  actual  inspection  of  the  isolated  compounds,  whether  one 
or  both  of  these  substances  is  contained  in  really  apprecia- 
ble quantity  in  the  substance  subjected  to  analysis.  If  only 
potassium  is  sought  for,  filter  the  aqueous  solution,  last 
mentioned,  though  a  very  small  filter,  add  to  the  filtrate  a 
drop  or  two  of  chlorhydric  acid  and  several  drops  of  a  solu- 
tion of  bichloride  of  platinum  (App.,  §  55).  A  yellow 
crystalline  precipitate  of  chloroplatinate  of  potassium  will 
separate  after  some  time.  Since  chloride  of  ammonium 
would  produce  a  similar  precipitate,  it  is,  of  course,  essential 
that  the  ammoniacal  salt  should  be  expelled  by  ignition  be- 
fore potassium  is  tested  for. 


§§  42,  43  ISOLATION  OF  CLASS   VII.  Gl 

In  case  sodium,  or  both  sodium  and  potassium,  be  sought 
for,  the  magnesium  must  first  be  got  rid  of.  To  this  end, 
moisten  the  dry  residue,  which  contains  the  chlorides  of  mag- 
nesium, of  potassium  and  of  sodium,  with  a  drop  or  two  of 
water,  mix  it  thoroughly  with  an  equal  bulk  of  red  oxide  of 
mercury  and,  ignite  the  mixture  until  fuming  ceases.  The 
chloride  of  magnesium  will  be  changed  to  oxide,  while  the 
easily  volatile  chloride  of  mercury  escapes  :  — 

MgCl2+HgO=MgO+HgCl2. 

The  ignition  should  be  effected  beneath  a  chimney,  or  in  a 
draught  of  air  powerful  enough  to  carry  away  the  poisonous 
fumes  of  the  corrosive  sublimate.  Boil  the  ignited  residue 
with  a  small  quantity  of  water  ;  separate  the  insoluble  oxide 
of  magnesium,  together  with  the  excess  of  oxide  of  mercury, 
by  filtration ;  evaporate  the  filtrate  to  a  small  bulk ;  throw 
down  the  potassium  as  chloroplatinate,  collect  the  latter  upon 
a  filter,  and  from  the  filtrate  remove  the  excess  of  chloride  of 
platinum  by  means  of  sulphuretted  hydrogen.  Filter  off  the 
sulphide  of  platinum,  and  evaporate  the  filtrate  to  dryness  to 
obtain  the  chloride  of  sodium.  Or,  instead  of  employing  sul- 
phuretted hydrogen,  evaporate  the  filtrate  from  the  chloropla- 
tinate of  potassium  in  a  watch  glass,  at  a  gentle  heat,  until  the 
liquid  begins  to  become  dry  at  its  edges,  and  then  examine  it 
with  a  magnifying  glass.  Characteristic  crystals  of  chloro- 
platinate of  sodium  will  be  seen  in  the  form  of  long,  slender 
prisms  or  needles  of  yellow  color. 

43.  The  Isolation  of  Class  VII,  by  the  removal  of  the 
preceding  classes,  has  been  described  in  §  12.  Care  must 
always  be  taken  to  concentrate  the  whole  of  the  filtrate  from 
Class  VI  by  evaporation,  before  testing  a  portion  of  it  for 
magnesium  ;  and  time  enough  must  be  allowed  for  the  mag- 
nesium precipitate  to  crystallize.  The  remainder  of  the 
filtrate  from  Class  VI  must  be  evaporated  to  dryness  and 
ignited,  before  testing  for  sodium  and  potassium,  in  order 
that  the  flame  reactions  of  these  elements  may  not  be  con- 

6 


62 


SEPARATION  OF  CLASSES. 


§44 


get 
ofa 


s 


w, 

B 


MI 


t! 


•a 
2  « 


A  residue 
indicates. 


A  precipitate 
indicates 


cc  -• 


§  44  /SEPARATION  OF  CLASSES.  63 

cealed  or  obscured  by  the  vapors  of  ammonium  salts,  or  by 
the  combustion  of  particles  of  organic  matter  derived  from 
the  various  reagents  which  have  been  added  in  the  course  of 
the  analysis. 

44.  An  outline  of  the  methods  employed  for  separating 
the  several  classes  is  presented  in  tabular  form  on  the  opposite 
page.  The  precautions  necessary  in  the  consecutive  exami- 
nation of  an  u  unknown  "  solution  for  the  members  of  the 
various  classes  have  been  already  given  under  the  several 
classes. 


I 

64  NON-METALLIC  ELEMENT^  §  45 


CHAPTER  IX 

GENEKAL  TESTS  FOB  THE    NON-METALLIC    ELEMENTS. 

45.  The  following  common  elements  remain  to  be  consid- 
ered :  —  Sulphur,  nitrogen,  phosphorus,  carbon,  boron,  silicon, 
chlorine,  bromine,  iodine,  fluorine,  oxygen,  hydrogen.  It  is 
obvious  that  oxygen  and  hydrogen  cannot  be  directly  sought 
for  by  any  analytical  process  conducted  in  the  wet  way. 
These  elements  are  added  to  the  original  matter  in  the  water 
or  acid  which  is  used  as  a  solvent.  The  presence  of  these 
elements  is  either  inferred  from  the  other  results  of  the 
analysis,  or  forms  the  object  of  direct  inquiry  in  the  prelimi- 
nary treatment,  —  that  important  part  of  every  analysis  which 
forms  the  main  subject  of  Part  II.  The  remaining  elements 
all  belong  to  that  class  vaguely  described  as  non-metallic; 
they  unite  with  oxygen,  hydrogen,  or  both  these  elements,  to 
form  what  are  commonly  called  acids. 

As  the  metallic  elements  are  recognized  through  familiar 
compounds,  hydrates,  chlorides,  sulphides,  or  other,  so  these 
non-metallic  elements  are  identified  by  working  out  of  the 
unknown  mixture  their  characteristic  compounds.  These 
compounds  are  generally  salts.  But  there  is  one  marked 
difference  between  the  search  for  the  metallic  and  the  search 
for  the  non-metallic  elements  in  the  wet  way.  In  the  case  of 
iron  and  mercury  it  is  commonly  necessary  to  determine 
whether  the  element,  if  present,  exists  as  a  ferrous  or  ferric, 
as  a  rnercurous  or  mercuric  salt ;  but  as  a  rule  it  is  true  that 
no  question  usually  arises  in  connection  with  the  determination 
of  a  metallic  element,  except  the  fundamental  one  of  its  pres- 
ence or  absence  in  a  given  solution.  The  sodium  in  the  three 


§  45  CLASSES  OF,  SALTS.  65 

different  salts,  sulphate,  sulphite  and  hyposulphite  of  sodium, 
for  example,  is  detected  by  one  and  the  same  method ;  but, 
when  the  other  elements  of  these  salts  are  sought  for,  three 
different  reactions  will  occur  according  to  the  varying  nature 
of  the  ingredients  other  than  sodium.  A  sulphate  in  solution 
gives  one  set  of  reactions,  a  sulphite  another,  and  a  hyposul- 
phite a  third.  It  is  important  to  do  more  than  determine  the 
mere  presence  of  sulphur  and  oxygen.  We  want  to  know 
whether  the  sodium  salt  be  a  sulphate,  sulphite,  or  hypo- 
sulphite. Analogous  questions  arise  with  regard  to  other 
non-metallic  elements  ;  there  is  chlorine  both  in  chlorides  and 
chlorates,  and  carbon  both  in  carbonates  and  oxalates. 
Arsenic,  too,  may  be  present  in  the  form  of  arsenite  or 
arseniate,  and  these  two  different  kinds  of  salts  exhibit 
many  quite  dissimilar  reactions. 

•  In  the  systematic  analysis  of  an  unknown  substance,  the  ex- 
amination for  the  metallic  elements  by  the  methods  detailed  in 
the  previous  chapter  invariably  precedes  the  determination  of 
the  non-metallic  elements.  Having  ascertained  which  of  the 
metallic  elements  are  present  in  the  substance  under  examina- 
tion, the  analyst  tries  to  identify  each  class  of  salts  which 
may  be  present  by  precipitating,  or  otherwise  making  mani- 
fest, some  familiar  member  of  that  class.  Thus  he  identifies 
sulphates  by  precipitating  sulphate  of  barium,  chlorides  by 
precipitating  chloride  of  silver,  carbonates  by  throwing 
down  carbonate  of  calcium,  and  so  forth.  The  practically 
important  inquiry  is,  how  to  find  means  of  identifying  each 
of  the  principal  classes  or  kinds  of  salts.  The  word  "  class  " 
or  "  kind  "  of  salts  is  used  in  this  connection  as  a  collective 
name  for  all  the  salts  which  may  be  regarded  as  derived  from 
one  and  the  same  acid  ;  thus  all  sulphates  constitute  one  class 
or  kind,  all  carbonates  another,  and  so  forth.  The  following 
common  classes  of  salts  are  those  for  which  more  or  less  per- 
fect means  of  recognition  will  be  given  in  this  chapter :  — 
Sulphates,  sulphites,  hyposulphites,  sulphides,  arseniates,  ar- 
senites,  phosphates,  carbonates,  oxalates,  tartrates,  borates, 


66          TESTING  FOE  NON-METALLIC  ELEMENTS.    §  45 

silicates,  chromates,  fluorides,  chlorides,  bromides,  iodides, 
cyanides,  nitrates,  chlorates,  acetates. 

No  system  of  successive  testing  and  elimination,  analogous 
to  that  already  described  for  the  metallic  elements,  has  been 
devised  for  the  non-metallic  constituents  of  salts.  There 
are,  indeed,  certain  so-called  general  reagents  for  acids;  but 
these  reagents  are  chiefly  useful  to  show  the  simultaneous 
presence  or  absence  of  members  of  several  classes  of  salts, 
and  hardly  help  towards  the  identification  of  any  individual 
class,  except  in  cases  of  the  simplest  sort,  in  which  only  a 
single  class  of  salts  is  represented. 

It  sometimes  happens  that  the  preliminary  examination 
(§  80,  81)  of  the  substance  to  be  analyzed  leads  directly  to 
some  conclusion  as  to  the  class  of  salts  in  hand.  A 
knowledge  of  the  metallic  element  or  elements  present  is 
moreover  in  most  cases  a  great  help  in  the  determination  of 
the  other  constituents.  It  is  for  this  reason  that  the  search  for 
the  metallic  elements  precedes  the  examination  for  the  non- 
metallic.  A  single  example  will  sufficiently  illustrate,  for  the 
present,  this  important  principle,  which  is  of  very  wide  ap- 
plication in  qualitative  analysis. 

Suppose  that  the  substance  under  examination  is  a  solid 
which  dissolves  without  difficulty  in  water  and  which  proves 
to  contain  barium.  From  the  presence  of  barium  in  a  com- 
pound soluble  in  water,  it  is  to  be  directly  inferred  that  there 
is  no  sulphate,  phosphate,  carbonate,  oxalate  or  tartrate  in 
the  original  substance  since  these  barium  salts  are  insoluble 
in  water.  The  list  of  salts  excluded  by  the  demonstrated 
presence  of  barium  would  be  very  long.  So  it  is  in  greater 
or  less  degree  with  many  other  metallic  elements.  It  is,  in- 
deed, no  easy  matter  to  make  a  solution  containing  even  one 
representative  of  the  seven  classes  into  which  the  metallic 
elements  have  been  divided,  because  each  of  these  elements, 
except  sodium  and  potassium,  when  present  in  a  solution 
excludes  one  or  more  whole  classes  of  salts.  By  attending 
to  just  inferences  to  be  drawn  from  the  quality  of  the  metallic 


§§  46,  47  THE  BARIUM  TEST.  67 

elements,  much  time  will  be  saved,  and  the  want  of  a  sys- 
tematic procedure  in  searching  for  the  non-metallic  elements 
will  be  little  felt.  The  presence  of  the  arsenites  and  arsen- 
iates,  of  carbonates,  chromates,  cyanides,  sulphides,  sulphites 
and  hyposulphites  will  ordinarily  be  revealed  in  the  course 
of  the  search  for  the  metallic  elements. 

Before  giving  the  special  tests  by  which  the  above-men- 
tioned classes  of  salts  are  identified,  we  proceed  to  describe 
certain  general  tests  which  are  of  value,  particularly  when 
they  give  negative  results. 

48.  The  Barium  Test.  —  When  a  solution  of  chloride 
(or  nitrate)  of  barium  is  added  in  suitable  quantity  to  a 
neutral  or  slightly  alkaline  solution  containing  representatives 
of  any  or  all  of  the  following  classes  of  salts,  precipitation 
usually  occurs,  for  all  these  salts  of  barium  are  insoluble  in 
water  and  alkaline  liquids,  if  no  ammonium  salts  be  pres- 
ent:— 

Sulphates,  Phosphates,  Silicates, 

Sulphites,  Carbonates,  Chromates, 

Hyposulphites,  Oxalates,  Fluorides. 

Arseniates,  Tartrates, 

Arsenites,  Borates, 

If  the  chloride  (or  nitrate)  of  barium  fail  to  produce  a 
precipitate  under  the  prescribed  conditions,  the  complete 
absence  of  all  the  above  thirteen  classes  of  salts  is  at  once 
demonstrated,  provided  that  no  ammonium  salts  be  contained 
in  the  original  solution. 

47.  Illustration  of  the  Barium  Test.  —  Prepare  in  a 
test-tube  a  solution  containing  at  once  sulphate,  phosphate 
and  carbonate  of  sodium  ;  a  very  small  bit  of  each  salt  will 
be  sufficient.  The  solution  will  be  found  to  be  alkaline  to 
litmus  paper.  Add  to  it  chloride  of  barium  (App.,  §  43), 
little  by  little,  until  a  fresh  addition  of  the  reagent 
no  longer  produces  an  additional  precipitate.  The  white 
precipitate  consists  of  sulphate,  phosphate  and  carbonate  of 


68  THE  BARIUM  TEST.  §  48 

barium.  All  the  thirteen  barium  salts  which  are  liable  to 
precipitation  under  these  circumstances  are  white,  with  the 
single  exception  of  chromate  of  barium.  The  yellow  color 
of  the  chromate  of  barium  (§  38)  distinguishes  this  one  pre- 
cipitate from  all  the  rest.  If  this  color  is  well  marked,  the 
presence  of  a  chromate  in  the  original  solution  (which  must 
also  have  been  }Tellow)  may  be  inferred  with  certainty.  In 
all  other  cases,  however,  the  precipitate  is  white,  as  in  the 
present  experiment.  The  next  question  is,  can  anything 
further  be  learned  from  this  white  precipitate? 

Add  to  the  contents  of  the  test-tube  dilute  chlorhydric 
acid,  until  the  liquid  has  a  decidedly  acid  reaction  to  litmus 
paper.  An  effervescence  indicates  the  escape  of  carbonic 
acid,  displaced  by  the  less  volatile  chlorhydric  acid.  The 
bulky  precipitate  which  the  chloride  of  barium  produced  will 
in  part  disappear,  but  a  portion  of  it  remains  undissolved. 
Filter  the  contents  of  the  tube.  The  particles  of  precipitated 
sulphate  of  barium  are  so  very  fine  that  they  often  pass 
through  the  pores  of  the  paper,  necessitating  repeated  filtra- 
tion through  the  same  filter.  To  the  filtrate  add  ammonia-water 
until  the  liquid  has  an  alkaline  reaction.  A  precipitate  will 
reappear :  the  phosphate  of  barium  which  was  dissolved  by 
the  chlorhydric  acid  is  reprecipitated  as  soon  as  the  acid 
solvent  is  neutralized  by  ammonia-water. 

48.  Of  all  the  barium  salts  which  might,  in  an  actual 
analysis,  be  precipitated  under  conditions  similar  to  those  of 
the  preceding  experiment,  only  one,  the  sulphate  of  barium, 
is  insoluble  in  chlorhydric  and  other  strong  acids.  A  separ- 
ation of  sulphur  from  a  hyposulphite  will  not  be  mistaken  for 
a  barium  precipitate  (§  19,  p.  20).  The  fact  that  any  of  the 
original  precipitate  remains  undissolved  by  the  chlorhydric 
acid  demonstrates  the  presence  of  a  sulphate.  The  portion 
of  the  original  precipitate  which  dissolved  in  the  acid,  and 
was  reprecipitated  by  ammonia,  consisted  in  this  particular 
experiment  of  phosphate  of  barium  ;  but  in  an  actual  analysis 
the  possible  salts  represented  would  be  so  numerous  as  to 
make  the  indication  of  but  little  value. 


§  48  THE  BAEIUM  TEST.  (59 

If  ammonia-water  should  cause  no  precipitation  in  the  acid 
liquid  which  was  filtered  from  the  original  precipitate,  it  must 
not  be  inferred  that  the  acid  of  course  dissolved  nothing. 
The  borate,  oxalate,  arseniate,  arsenite,  tartrate  and  fluoride 
of  barium  are  all  moderately  soluble  in  solutions  of  ammo- 
niacal  salts,  and  may  not  be  precipitated  on  the  addition  of 
ammonia.  Of  course,  if  the  original  solution  contained  am- 
monium salts,  these  six  barium  salts,  if  present  in  small 
quantity  only,  might  fail  to  be  precipitated.  In  fact,  all  the 
thirteen  above-mentioned  barium  salts,  except  the  sulphate, 
are  more  or  less  soluble  in  solutions  of  ammonium  salts,  so 
that,  whenever  ammonium  salts  are  known  to  be  present, 
there  is  really  but  one  perfectly  satisfactory  indication  with 
chloride  of  barium.  The  presence  of  a  sulphate  is  revealed 
by  it  with  certainty,  but  the  results  of  the  other  tests  must 
be  received  with  some  distrust. 

If  the  original  solution  be  acid,  it  is  necessary  to  neutralize 
it  with  ammonia-water  before  the  chloride  of  barium  is  added. 
Sometimes  a  precipitate  is  produced  by  the  ammonia-water 
so  added ;  in  that  case  it  is  necessary  to  filter  and  proceed 
with  the  filtrate,  although  the  ammonia-water  may  have 
thrown  down  salts  of  several  of  the  classes  above  named, 
such  as  phosphates,  oxalates  and  fluorides.  (See  also  §  28, 
p.  37.)  Even  if  the  ammonia-water  produce  no  precipitate, 
the  testing  is  then  performed  under  the  disadvantage  of  the 
presence  of  ammonium  salts. 

If  the  original  solution  contained  silver  or  lead  salts,  or 
mercurous  salts,  it  would  be  impossible  to  use  chloride  of 
barium  and  chlorhydric  acid  as  reagents ;  they  would  throw 
down  the  chlorides  of  those  metals.  Nitrate  of  barium 
(App.,  §  44)  and  dilute  nitric  acid  must  then  be  used. 

The  acids  added  to  the  precipitate  formed  by  the  barium 
salt  must  be  always  dilute  acids.  Chloride  and  nitrate  of 
barium  are  themselves  insoluble  in  concentrated  chlorhydric 
and  nitric  acids,  and  if  a  strong  acid  were  used  as  a  solvent, 
the  reagent  salt  might  itself  separate  from  the  liquid. 


70  THE  CALCIUM  TEST.  §§  49,  5Q 

49.  The  Calcium  Test.  —  Chloride  (or  nitrate)  of  cal- 
cium precipitates  the  same  classes  of  salts  as  chloride  (or 
nitrate)  of  barium,  with  the  single  exception  of  the  chro- 
inates.     When  sulphates  and  all  ammoniacal  salts  are  absent, 
or  present  only  in  minute   quantities,  something  may  be 
learned  by   testing  a  neutral  or  slightly  alkaline    solution 
supposed  to  contain  representatives  of  some  of  the  other 
classes  of  salts  enumerated  in  §  46,  with  chloride  or  nitrate 
of  calcium.     The  calcium  salts  liable  to  precipitation  under 
these  circumstances  are  all  soluble  in  acetic  acid,  except  the 
oxalate  and  the  fluoride.     The  precipitate  produced  by  the 
calcium  reagent  is,  therefore,  treated  with  acetic  acid ;  if  it 
completely  redissolves,  oxalates  and  fluorides  are  most  prob- 
ably absent.     The  presence  of  notable  quantities  of  ammo- 
nium salts  renders  this  test  of  uncertain  value ;  because  the 
fluoride   and  many   other   salts   of  calcium   are   soluble   in 
solutions  of  ammonium  salts.     Since  sulphate  of  calcium  is 
sparingly  soluble  in  water  and  acetic  acid,  the  presence  of  a 
sulphate,  causing  precipitation  of  sulphate  of  calcium,  ob- 
scures the  reaction  for  oxalates  and  fluorides.     Nitrate  of 
calcium  must  be  used  instead  of  the  chloride  whenever  silver 
or  lead  salts,  or  mercurous  salts,  are  present  in  the  solution 
under  examination. 

50.  Illustration  of  the  Calcium  Test.  —  Prepare  in  a 
test-tube  an  aqueous  solution  of  phosphate,  oxalate  and  tar- 
trate  of  sodium  or  potassium.     A  very  small  quantity  of  each 
salt  will  be  enough.    The  solution  will  be  neutral  or  faintly 
alkaline.     Add  to  this  solution  a   solution  of  chloride  of 
calcium    (App.,   §   42)   until  the  precipitation  is  complete. 
Collect  the  white  precipitate  upon  a  filter,  and,  when  drained, 
transfer  it  to  a  test-tube  and  treat  it  with  acetic  acid.     The 
phosphate  and  tartrate  of  calcium  will  redissolve,  but  the 
oxalate  remains  untouched.     To  verify  this  result,  and  iden- 
tify each  one  of  the  classes  of  salts  present  in  the  original 
solution,  special  tests,  to  be  hereafter  described,  must  be 
resorted  to. 


§§  51,  52  THE  SILVER   TEST.  71 

51.  The  Silver  Test.  —  Nitrate  of  silver  produces  a  pre- 
cipitate in  neutral  or  acid  solutions  with  all  chlorides,  bro- 
mides, iodides  and  cyanides,  and  in  neutral  solutions  with 
most  of  the  classes  of  salts  enumerated  in  §  46.     In  order  to 
obtain  the  most  comprehensive  negative  conclusion  in  the 
case  that  nitrate  of  silver  produces  no  precipitate,  it  is  nec- 
essary to  operate  upon  a  neutral  solution.     If,  on  the  addi- 
tion of  nitrate  of  silver  to  a  neutral  solution,  no  precipitate 
appears  after  the  lapse  of  several  minutes,  neither  chlorides, 
bromides,  iodides,    cyanides  nor  sulphides  can  be  present, 
and  the  absence  of  sulphites,  hyposulphites,  carbonates,  phos- 
phates, arseniates,  arsenites,  chromates,  silicates,  oxalates 
and  tartrates  may  also  be  inferred  with  considerable  cer- 
tainty. 

52.  Illustration  of  the  Silver  Test.  —  Prepare  in  a  test- 
tube  a  weak  solution  of  chloride  of  sodium,  iodide  of  potas- 
sium, cyanide  of  potassium  and  phosphate  of  sodium.     Add 
nitrate  of  silver  (App.,  §  39)  to  this  slightly  alkaline  solu- 
tion, until  the  precipitation  is  complete.     The  dense  precipi- 
tate  is   yellowish-white.      Pour  dilute  nitric  acid  into  the 
mixture,  until  the  solution  is  strongly  acid ;   shake  up  the 
contents  of  the  tube  thoroughly,  and  after  the  lapse  of  several 
minutes    collect  the  insoluble    precipitate    on  a  filter,  and 
receive  the  filtered  liquid  in  a  test-tube. 

Neutralize  the  filtrate  with  ammonia-water :  a  yellow  pre- 
cipitate of  phosphate  of  silver  will  reappear. 

Wash  the  precipitate  on  the  filter  thoroughly  to  free  it  from 
the  superfluous  nitrate  of  silver.  Rinse  the  washed  precipi- 
tate into  a  clean  test-tube,  decant  the  water  from  above  it, 
pour  over  it  ammonia-water,  and  gently  heat  the  mixture. 
The  silver  precipitate  will  visibly  diminish  in  bulk,  but  a  yel- 
lowish portion  remains  undissolved.  Filter  again,  and  neu- 
tralize the  filtrate  with  nitric  acid ;  a  white  precipitate  will 
fall. 

This  experiment  proves  that  a  portion,  but  not  all,  of  the 
mixed  silver  salts  which  are  insoluble  in  nitric  acid,  are  solu- 


72  THE  SILVER    TEST.  §  53 

ble  in  ammonia-water.  The  chloride,  cyanide  and  bromide  of 
silver  dissolve  in  ammonia-water,  the  latter  with  difficulty ; 
the  iodide  remains  undissolved.  Special  tests,  hereafter  to 
be  described,  are  applied  in  order  to  confirm  the  presence  of 
iodine,  and  to  detect  each  and  all  of  the  three  substances  which 
are  liable  to  be  confounded  in  the  white  precipitate  just  men- 
tioned. 

53.  In  the  application  of  the  silver  test  to  the  examina- 
tion of  a  substance  of  unknown  composition,  it  is,  of  course, 
most  advantageous  to  work  with  a  neutral  solution,  as  in  such 
a  case  the  absence  of  any  precipitate  would  lead  to  the  infer- 
ence that  all  the  salts  mentioned  in  §  51  are  absent:  if  the. 
solution  is  neutral,  the  nitrate  of  silver  may  be  added  directly 
to  a  portion  of  it.  In  addition  to  the  classes  of  salts  men- 
tioned in  §  51,  if  the  original  solution  contained  any  consid- 
erable quantity  of  a  borate,  the  borate  of  silver  would  be 
precipitated  under  these  conditions ;  but  a  small  proportion 
of  some  borate  might  escape  precipitation.  If  the  original 
solution  be  acid  to  test  paper,  add  nitrate  of  silver  to  a  por- 
tion of  it  in  a  test-tube,  and  then  pour  in  upon  the  liquid 
some  dilute  ammonia-water,  so  gently  that  the  two  liquids  do 
not  mix  at  once.  At  some  layer  near  the  junction  of  the  two 
dissimilar  liquids,  the  fluid  must  be  neutral.  If  at  that  layer 
no  precipitate  or  cloud  appear,  the  twelve  kinds  of  salts  above 
enumerated  are  abselit.  If  the  original  solution  is  alkaline, 
dilute  nitric  acid  is  to  be  added  in  precisely  the  same  manner 
as  the  ammonia- water  in  the  opposite  case.  The  neutral 
layer  between  the  two  liquids  is  attentively  observed,  and  the 
absence  of  any  film  or  cloud  therein  justifies  the  same  sweep- 
ing conclusion  as  that  above  given. 

If  any  precipitate  is  produced  by  nitrate  of  silver,  its  color- 
is  to  be  observed,  for  some  conclusions  may  often  be  drawn 
from  this  color.  Chloride,  bromide,  cyanide,  oxalate,  tar- 
trate,  silicate  and  borate  of  silver  are  white ;  iodide,  phos- 
phate and  arsenite  of  silver  are  yellow  ;  arseniate  of  silver  is 
brownish-red ;  chromate  of  silver  is  purplish-red ;  sulphide 


§§  53,  54  THE  SILVEE   TEST.  73 

of  silver  is  black.  When  the  silver  precipitate  is  white, 
black,  or  of  some  obscure,  indecisive  color,  the  operations  in 
the  wet  way  at  this  stage  should  be  directed  to  proving  or 
disproving  the  presence  of  chlorides,  bromides,  iodides,  cy- 
anides and  sulphides.  To  this  end  the  portion  of  the  original 
solution  which  has  been  already  tested  with  nitrate  of  silver, 
sh6uld  be  made  decidedly  acid  with  dilute  nitric  acid.  Of  all 
the  silver  salts  which  can  be  precipitated  on  the  addition  of 
nitrate  of  silver,  only  the  chloride,  bromide,  iodide,  cyanide 
and  sulphide  can  resist  dilute  nitric  acid.  If  the  precipitate 
once  formed  redissolves  completely  in  nitric  acid,  no  chloride, 
bromide,  iodide,  cyanide  or  sulphide  was  present  in  the  orig- 
inal solution.  If,  on  the  contrary,  a  residue  remain,  one  or 
more  of  these  kinds  of  salts  must  have  been  represented  in 
the  original  solution.  If  the  residue  be  black  or  blackish, 
the  presence  of  a  sulphide  is  to  be  inferred  ;  if  it  be  white  or 
whitish,  the  absence  of  sulphides  and  the  presence  of  a 
chloride,  bromide  or  cyanide  is  to  be  inferred ;  if  it  be  dis- 
tinctly yellowish,  an  iodide  is  probably  present.  When  the 
liquid  under  examination  contains  a  ferrous  salt,  protochlo- 
ride  of  tin,  or  any  other  active  reducing  agent,  metallic  silver 
is  liable  to  be  precipitated  as  a  dark,  heavy  powder.  The 
examination  for  the  metallic  element  will  generally  have  re- 
vealed the  presence  of  any  such  agent. 

It  is  to  be  remarked  that  cyanide  of  mercury  does  not  give 
a  precipitate  with  nitrate  of  silver.  When  mercury  has  been 
detected  in  the  substance  under  examination,  cyanogen  must 
be  sought  for  in  other  ways  (§  58)  than  this. 

54.  Nitrates,  Chlorates  and  Acetates.  —  It  is  quite 
clear  that  no  method  of  precipitation  whatever  will  apply  to 
nitrates,  chlorates  and  acetates,  since  these  kinds  of  salts  are 
all  soluble.  No  insoluble  nitrate,  chlorate,  or  acetate  is 
known.  Special  tests  must  be  sought  for  these  three  classes 
of  salts. 


74  SPECIAL  TESTS.  §§55,56 


CHAPTER  X. 

SPECIAL  TESTS  FOR  THE   WOW-METALLIC  ELEMENTS. 

55.  We  now  proceed  to  indicate  the  most  available  special 
tests  for  the  non-metallic  elements  and  their  commonest  com- 
pounds.    It  is  noteworthy  that  the   non-metallic   elements 
enter  into  composition  under  various  forms,  which  produce, 
with  one  and  the  same  metallic  element,  various  salts.     Thus 
within  the  narrow  range  of  this  treatise,  sulphur  is  to  be 
sought  in  sulphides,  sulphates,  sulphites  and  hyposulphites ; 
carbon  in  cyanides,  acetates,  carbonates,  oxalates  and  tar- 
trates,  and  arsenic  in  arsenites  and  arseniates.     The  various 
classes  of  salts  will  be  taken  up  successively.     It  should  be 
premised  that  these  special  tests  are  sometimes  applied  to 
the  original  solution  before  the  precipitation  with  chloride  of 
barium  and  fcitrate  of  silver,  and  sometimes  during  or  after 
these  more  general  testings.     In  the  first  case,  the  student  is 
seeking  guidance  in  the  application  of  the  more  comprehen- 
sive tests  ;  in  the  latter  case,  he  is  trying  to  confirm  results 
already  almost  sure. 

56.  Effervescence.  —  When  a  solution  containing  a  car- 
bonate,  cyanide,  sulphide,   sulphite,   or  hyposulphite,  or  a 
mixture  of  representatives  of  some  or  all  of  these  kinds  of 
salts,  is  treated  with  chlorhydric  acid  and  then  warmed,  an 
evolution  of  gas  occurs  with  more  or  less  effervescence.     The 
gases  evolved  are  all  colorless ;  but  they  all  have  very  char- 
acteristic odors  except  carbonic  acid,  the  gas  which  escapes 
from  a  carbonate.     A  cyanide  gives  off  the  pungent  odor  of 
cyanhydric  acid.     A  sulphide  yields  sulphuretted  hydrogen 
of  familiar  presence.    Sulphurous  acid  escapes  from  sulphites 


§  §  57,  58          CAEBONATES.  —  CYANIDES.  75 

and  hyposulphites  alike ;  but  in  the  latter  case  a  deposition 
of  sulphur  makes  the  liquor  turbid.  If  only  one  of  these 
gases  were  present,  the  effervescence  and  the  odor,  or  the 
absence  of  odor,  would  identify  it ;  but  when  mixtures  are  to 
be  dealt  with,  further  means  of  identification  are  necessary. 

57*  Carbonates.  —  To  prove  the  presence  of  carbonic 
acid  gas,  when  effervescence  has  occurred,  add  chlorhydric 
acid,  little  by  little,  to  the  effervescing  solution,  until  the  acid 
is  decidedly  in  excess  ;  meanwhile  keep  the  mouth  of  the  test- 
tube  loosely  closed  with  the  thumb  to  promote  the  accumula- 
tion of  the  gas  evolved.  When  the  tube  is  supposed  to  be 
fall,  carefully  decant  the  gas  into  a  second  test-tube  contain- 
ing a  teaspoonful  of  lime-water  (App.,  §  41),  taking  care 
not  to  allow  any  of  the  liquid  to  pass  over  with  the  gas. 
Mix  the  lime-water  and  the  gas  in  the  second  test-tube  by 
thorough  shaking.  A  white  precipitate  of  carbonate  of  cal- 
cium will  be  produced,  if  the  gas  tested  is,  or  contains,  car- 
bonic acid. 

If  the  effervescence  is  slight,  and  the  quantity  of  gas 
evolved  seems  too  small  to  be  decanted  in  this  wajr,  dip  the 
end  of  a  dark-colored  glass  rod  into  lime-water,  and  thrust 
the  moistened  end  into  the  test-tube,  bringing  it  close  to  the 
surface  of  the  fluid.  If  the  gas  be  carbonic  acid,  the  lime- 
water  adhering  to  the  rod  will  become  visibly  turbid. 

The  student  who  desires  to  see  the  working  of  this  test 
before  having  occasion  to  apply  it  in  an  actual  analysis,  can 
operate  upon  a  morsel  of  carbonate  of  sodium  dissolved  in  a 
little  water. 

58-  Cyanides.  —  When  the  smell  of  the  gas  which  es- 
capes from  the  solution  under  examination  (§  56),  or  the 
qualities  of  the  precipitate  with  nitrate  of  silver  (§  53),  give 
occasion  to  suspect  the  presence  of  a  cyanide,  the  following 
confirmatory  test  may  be  resorted  to  :  —  Add  to  the  solution 
supposed  to  contain  free  cyanhydric  acid,  or  an  alkaline 
cyanide,  a  few  drops  of  a  solution  containing  both  a  ferrous 
and  a  ferric  salt  (a  solution  of  ferrous  sulphate  which  has 


76  SULPHIDES.  — SULPHITES.  §§  59,  60 

been  exposed  to  the  air,  for  example),  and  a  small  quantity 
of  caustic  soda  solution.  If  cyanogen  is  present,. a  bluish- 
green  precipitate  forms,  which  consists  of  a  mixture  of  Prus- 
sian blue  and  the  hydrates  of  iron.  Warm  the  liquid,  and 
add  to  it  an  excess  of  chlorhydric  acid.  The  hydrates  of  iron 
dissolve,  but  the  Prussian  blue  remains  undissolved. 

In  case  the  proportion  of  cyanogen  is  small,  the  precip- 
itated hydrates  of  iron  may  conceal  the  Prussian  blue  until 
the  addition  of  the  acid ;  and  in  the  case  of  minute  quan- 
tities the  liquid  simply  appears  green  after  the  addition  of 
chlorhydric  acid,  and  it  is  only  after  long  standing  that  a 
trifling  blue  precipitate  separates  from  it. 

This  test  may  be  well  illustrated  by  means  of  a  small  particle 
of  cyanide  of  potassium  dissolved  in  a  teaspoonful  of  water. 

To  detect  cyanogen  in  cyanide  of  mercury,  it  is  necessary 
to  precipitate  the  mercury  as  sulphide,  by  means  of  sulphur- 
etted hydrogen,  and  to  identify  the  free  cyanhydric  acid  in 
the  filtered  or  decanted  fluid. 

59.  Sulphides.  —  Many  sulphides  give  off  sulphuretted 
hydrogen  when  heated  with  chlorhydric  acid.     If  the  quan- 
tity of  gas  is  so  small  that  its  odor  is  imperceptible,  the  lead 
paper  test  (§32)  should  be  applied. 

When  sulphides  are  dissolved  in  nitric  acid  or  aqua  regia, 
their  sulphur  is  partly  separated  in  a  free  state  and  partly 
converted  into  sulphuric  acid.  The  free  sulphur  is  identified 
by  its  color  and  texture,  and  by  its  behavior  when  burnt. 
The  sulphuric  acid  in  the  liquid  is  detected  in  the  usual 
manner  (§  64). 

60.  Sulphites.  —  All  the  sulphites   evolve   sulphurous 
acid,  without  any  deposition  of  sulphur,  when  treated  with 
chlorhydric  acid.     The  very  sharp  odor  of  this  gas  is  enough 
to  identify  it. 

As  has  been  before  stated,  nitrate  of  silver  produces  in 
solutions  of  sulphites  a  white  precipitate ;  but  this  precip- 
itate blackens  when  the  liquid  is  boiled,  on  account  of  the 
reduction  of  silver. 


§§61,62     HYPOSULPHITES.—  CHROMATES.  77 

When  the  sulphites  are  heated  with  strong  nitric  acid,  or 
other  powerful  oxidizing  agent,  they  are  converted  into  sul- 
phates without  precipitation  of  sulphur.  The  sulphates  so 
produced  may  be  identified  in  the  usual  way  (§  64). 

61.  Hyposulphites.  —  The  hyposulphites  disengage  sul- 
phurous acid  and  deposit  sulphur  when  warmed  with  chlor- 
hydric  acid.    This  decomposition  is   not  immediate  if  the 
solution  be  dilute. 

The  precipitate  produced  in  the  solution  of  a  hyposulphite 
by  nitrate  of  silver,  dissolves  again  readily  in  an  excess  of 
the  hyposulphite.  On  standing,  the  precipitate  of  hyposul- 
phite of  silver  turns  black  spontaneously,  being  decomposed 
into  sulphide  of  silver  and  sulphuric  acid.  Heating  produces 
this  effect  almost  immediately. 

Hyposulphite  of  sodium  is  a  good  salt  from  which  to  get 
the  above  reactions  of  hyposulphites. 

62.  Chromates.  —  Chromium  is  detected  during  the  ex- 
amination for  the  metallic  elements,  and  the  analyst  generally 
obtains  pretty  certain  evidence  concerning  the  actual  con- 
dition   in    which   this    element   enters   into    the   substance 
under  examination,  whether  as  chromate  or  salt  of  chromium  ; 
for  the  chromates    are    reduced  by  sulphuretted  hydrogen 
with  change  of  color  and  deposition  of  sulphur  as  stated  in 
§  23. 

To  confirm  the  indications  thus  obtained,  the  following  tests 
are  used :  —  When  acetate  of  lead  (App.,  §  45)  is  added  to 
a  neutral  solution  of  a  chromate,  yellow  chromate  of  lead 
separates,  insoluble  in  acetic  acid,  but  soluble  in^caustic 
soda. 

As  has  been  before  stated,  the  purplish-red  color  of  chro- 
mate of  silver  (§  53),  and  the  yellow  color  of  chromate  of 
barium  (§  48),  are  valuable  indications  of  the  presence  of  a 
chromate. 

A  solution  of  normal  chromate  of  potassium  is  the  best 
substance  from  which  to  obtain  for  the  first  time  the  reactions 
of  the  chromates. 


78  ARSENITE8.  —  ARSENIATES.        §§63,  64 

63.  Arsenites  and  Arseniates.  —  The  presence  or  ab- 
sence of  arsenic  is  determined  in  the  search  for  the  metallic 
elements  by  the  tests  already  given  in  the  treatment  of 
Class  III.  These  tests,  however,  do  not  indicate  which  class 
of  compounds  (arsenic  or  arsenipus)  is  present  in  the  solu- 
tion under  examination.  In  whatever  form  present,  the 
arsenic  would  be  precipitated  as  the  tersu7phide  (As2S3),  and 
subsequently  converted  into  an  arseniate  by  fusion  with  ni- 
trate of  sodium.  Discriminating  tests  must  therefore  be 
applied  to  the  original  solution. 

^The  tests  by  which  an  arseniate  may  be  identified  have 
already  been  given  (§§  2£,  p.  31).  It  may  be  remarked  fur- 
ther that  the  presence  of  this  class  of  arsenic  compounds 
is  often  inferred  by  the  length  of  time  required  to  saturate 
with  sulphuretted  hydrogen  a  solution  containing  arsenic 
acid  or  an  arseniate.  The  arsenic  acid  is  first  reduced  to 
arsenious  acid  and  then  precipitated ;  a  separation  of  sulphur 
accompanies  the  reduction. 

A  solution  of  an  arsenite  yields  with  nitrate  of  silver  a 
yellow  precipitate  of  arsenite  of  silver  under  the  same  con- 
ditions in  which  an  arseniate  gives  the  brownish-red  precip- 
itate. The  silver  test  generally  serves  to  distinguish  between 
arsenites  and  arseniates,  but  circumstances  may  arise  in 
which  it  would  be  inapplicable.  The  following  test  affords 
further  means  of  discrimination  :  — 

If  to  a  solution  of  arsenious  acid  or  an  arsenite,  caustic 
soda  be  first  added  in  excess,  and  then  five  or  six  drops  of  a 
dilute  solution  of  sulphate  of  copper,  a  clear  bluish  liquid  is 
obtained,  which,  upon  boiling,  deposits  a  red  precipitate  of 
suboxide  of  copper  (Cu2O),  while  soluble  arseniate  of  sodium 
is  simultaneously  produced,  and  remains  in  the  solution. 
This  test  is  good  as  a  means  of  distinguishing  between 
arsenites  and  arseniates  when  no  organic  matters  are  con- 
tained in  the  solution  under  examination.  The  qualification 
is  necessary,  because  grape-sugar  and  many  other  organic 
substances  exercise  a  like  reducing  action  on  copper  salts. 


§  65  PHOSPHATES.  79 

64.  Sulphates.  — The  barium  test  (§§  46-48)  is  all  suf- 
ficient for  the  detection  of  sulphates.     The  operator  should 
make  sure  that  the  chlorhyclric  acid  itself  contains  no  sul- 
phuric acid,  that  an  excess  of  acid  is  really  present,  and  that 
the  solution  is  tolerably  dilute.     Concentrated   acids   and 
strong  solutions  of  many  salts  impair  the  delicacy  of  the 
reaction. 

65.  Phosphates.  —  When  the  previous  steps  of  the  anal- 
ysis have  proved  that  the  phosphates  present  in  the  solution 
under  examination  are  soluble  in  ammoniacal  liquids,  and 
that  no  arsenic  acid  or  arseniates  are  present,  the  following 
test  will  identify  a  phosphate  or  free  phosphoric  acid. 

Add  to  the  solution  to  be  tested  a  clear  mixture  of  sulphate 
of  magnesium,  chloride  of  ammonium  and  ammonia-water. 
"When  a  phosphate  or  free  phosphoric  acid  is  present,  a  white, 
crystalline  precipitate  of  phosphate  of  magnesium  and  ammo- 
nium is  formed,  even  in  very  dilute  solutions.  Stirring  and 
shaking  promote  its  separation.  The  precipitate  dissolves 
readily  in  acids. 

When  arsenic  acid  or  arseniates  are  present  in  the  original 
mixture,  this  test  for  phpsphates  can  still  be  applied,  if  all 
the  arsenic  be  previously  removed  by  precipitation  as  sulphide 
(§  24).  The  magnesium  mixture  can  be  used  in  the  filtrate 
from  the  sulphide  of  arsenic,  after  it  has  been  boiled  to  expel 
the  sulphuretted  hydrogen. 

The  preceding  test  can  only  be  applied  when  the  phosphate 
present  is  soluble  in  ammoniacal  solutions.  The  following 
test  is  of  much  more  general  application ;  it  can  be  used  in 
presence  of  arsenic  acid,  and  is  applicable  to  either  neutral 
or  acid  solutions  of  phosphates ;  it  is  also  extremely  deli- 
cate. 

When  two  or  three  drops  of  a  neutral  or  acid  solution  of  a 
phosphate  (even  of  iron,  aluminum,  barium,  strontium,'  cal- 
cium or  magnesium  [compare  §  28])  are  poured  into  a  test- 
tube  containing  four  or  five  teaspoonfuls  of  a  solution  of 
molybdate  of  ammonium  in  nitric  acid  (App.,  §  21),  there  is 


80  OXALATES.— 'TARTBATES.  §§66,67 

formed  in  the  cold  a  pale-yellow  precipitate  which  is  apt  to 
gather  upon  the  sides  and  bottom  of  the  tube.  If  the  pre- 
cipitate does  not  appear  in  a  few  minutes,  a  few  drops  more 
of  the  solution  to  be  tested  may  be  added.  This  precipitate 
is  soluble  in  an  excess  of  phosphoric  and  other  acids ;  and 
certain  organic  substances  also  prevent  its  formation.  A 
yellow  coloration  of  the  liquid  merely  is  not  enough  to  prove 
beyond  question  the  presence  of  a  phosphate  ;  a  precipitate 
must  be  waited  for.  The  yellow  precipitate  can  be  easily 
recognized,  even  in  dark-colored  liquids,  when  it  has  settled. 
The  solution  to  be  tested  must  not  be  heated,  nor  must  it  be 
more  than  blood-warm. 

Phosphate  of  sodium  is  the  best  substance  on  which  to  try 
the  test  for  phosphates. 

66.  Oxalates. — The  precipitation  of  white,  finely-divided 
oxalate  of  calcium,  by  all  soluble  calcium  salts  from  solutions 
of  oxalates  or  oxalic  acid,  has  been  already  described  (§  50). 
Even  the  solution  of  sulphate  of  calcium  gives  this  reaction 
with  oxalates. 

If  oxalic  acid,  or  an  oxalate  in  the  dry  state,  be  heated  in 
a  test-tube  with  an  excess  of  concentrated  sulphuric  acid,  a 
mixture  of  carbonic  oxide  and  carbonic  acid  is  set  free  with 
effervescence ;  the  carbonic  acid  may  be  identified  by  the 
lime-water  test ;  and  if  the  quantity  operated  upon  is  con- 
siderable, the  carbonic  oxide  may  be  inflamed  at  the  mouth 
of  the  tube. 

67.  Tartrates.  —  Tartaric  acid  and  the  tartrates,  when 
heated  in  the  dry  state,  char,  and  emit  a  very  characteristic 
odor  which  somewhat  resembles  that  of  burnt  sugar.     Strong 
sulphuric  acid  blackens  tartaric  acid  and  the  tartrates.     This 
is  the  only  class  of  salts  among  all  those  within  the  scope  of 
this  treatise,  which  exhibit  this  carbonization  by  sulphuric 
acid. 

To  confirm  the  presence  of  tartaric  acid,  or  a  tartrate,  in 
any  liquid  supposed  to  contain  it,  a  concentrated  solution  of 
acetate  of  potassium  is  added  to  the  liquid,  and  the  mixture 


§  6  8  TAB  TRA  TES.  —  B  OR  A  TES.  8 1 

violently  shaken.  The  precipitate,  when  one  forms,  is  a  diffi- 
cultly soluble  acid  tartrate  of  potassium.  The  addition  of  an 
equal  volume  of  alcohol  increases  the  delicacy  of  the  reaction. 
The  more  concentrated  the  solution  to  be  tested  the  better. 
To  prepare  the  required  solution  of  acetate  of  potassium  at 
the  moment  of  use,  rub  together  in  a  dish  half  a  teaspoonful 
of  carbonate  of  potassium  and  as  many  drops  of  acetic  acid 
as  will  dissolve  three  quarters  of  the  carbonate ;  throw  the 
mixture  on  a  small  moistened  filter  and  use  the  filtrate. 

Tartaric  acid  is  a  good  substance  from  which  to  get  these 
reactions. 

68.  Borates.  —  To  confirm  the  presence  of  a  borate, 
strong  sulphuric  acid  is  mixed  with  the  dry  substance  under 
examination  in  quantity  sufficient  to  make  a  thin  paste,  and 
an  equal  bulk  of  alcohol  is  added  to  the  mixture.  The  alco- 
hol is  then  kindled.  Boracic  acid  imparts  to  the  alcohol 
flame  a  yellowish-green  color.  The  test  is  made  more  deli- 
cate by  stirring  the  mixture,  and  by  repeatedly  extinguishing 
and  rekindling  the  flame.  Copper  salts  impart  a  somewhat 
similar  color  to  the  flame  ;  but  this  metal,  if  present,  may  be 
got  rid  of  by  sulphuretted  hydrogen  before  testing  for  boracic 
acid. 

If  a  solution  of  boracic  acid,  or  of  a  colorless  borate,  is 
mixed  with  chlorhydric  acid  to  slight,  but  distinct,  acid  reac- 
tion, and  a  slip  of  turmeric  paper  is  dipped  half  way  into  the 
liquid  and  then  dried  at  100°  C.,  the  dipped  half  shows  a 
peculiar  red  tint.  This  test  is  delicate,  but  there  are  a  few 
other  solutions  which  impart,  not  the  same,  but  somewhat 
similar  tints  to  turmeric  paper.  The  yellow  turmeric  paper 
used  for  this  test  is  prepared  by  steeping  narrow  strips  of 
white  paper  in  a  filtered  tincture  of  turmeric  root.  The  dried 
paper  should  have  a  fine  yellow  color.  The  tincture  is  made 
by  digesting  one  part  of  bruised  turmeric  in  six  parts  of 
warm  spirits  of  wine. 

The  reactions  of  borates  may  be  obtained  with  a  fragment 
of  borax. 


82  SILICA  TES.  —  FL  UORIDES.  §§69,70 


Silicates.  —  The  silicates  of  sodium  and  potassium 
are  the  only  silicates  which  are  soluble  in  water.  The  solu- 
tions of  these  alkaline  silicates  are  decomposed  by  all  acids. 
If  chlorhydric  acid  is  added  gradually  to  a  strong  solution  of 
an  alkaline  silicate,  the  greater  part  of  the  silicic  acid  separ- 
ates as  a  gelatinous  hydrate.  As  a  rule,  the  more  dilute  the 
fluid,  the  more  silicic  acid  remains  in  solution. 

If  the  solution  of  an  alkaline  silicate,  mixed  with  chlorhy- 
dric or  nitric  acid  in  excess,  be  evaporated  to  dryness,  silicic 
acid  separates  ;  if  the  dry  mass  be  ignited  and  then  treated 
with  dilute  chlorhydric  or  nitric  acid,  the  whole  of  the  silicic 
acid  remains  insoluble  in  the  free  state,  as  a  gritty,  whitish 
powder,  while  the  other  substances  dissolve. 

A  solution  of  chloride  of  ammonium  produces  a  gelatinous 
precipitate  in  strong  and  moderately  dilute  solutions  of  the 
alkaline  silicates.  This  precipitate  is  hydrated  silicic  acid 
containing  alkali. 

A  solution  of  waterglass  is  the  best  substance  in  which  to 
study  the  reactions  of  the  silicates  of  the  alkali-metals. 

~l70-r-  Fluorides.  —  If  a  finely-pulverized  fluoride  is  heated 
with  concentrated  sulphuric  acid  in  a  small  leaden  capsule  or 
platinum  crucible,  fluorhydric  acid  is  disengaged. 

Coat  with  wax  the  convex  face  of  a  watch-glass  large 
enough  to  cover  the  capsule,  by  heating  the  glass  cautiously, 
and  spreading  a  small  bit  of  wax  evenly  over  it  while  the 
glass  is  hot.  Trace  some  lines  or  letters  through  the  wax 
with  a  pointed  instrument  of  wood  or  horn.  Fill  the  hollow 
of  the  glass  with  cold  water,  and  cover  with  it  the  capsule 
which  contains  the  fluoride  mixture.  Heat  the  capsule  gently 
for  half  an  hour  or  an  hour.  Then  remove  the  watch-glass, 
dry  it,  heat  it  cautiously  to  melt  the  wax,  and  wipe  it  with  a 
bit  of  paper.  The  lines  or  letters  traced  through  the  wax 
will  be  found  etched  into  the  glass.  A  barely  perceptible 
etching  is  made  more  visible  by  breathing  upon  the  glass. 
If  much  silicic  acid  is  present,  this  reaction  fails. 

When  a  fluoride,  naturally  combined  or  artificially  mixed 


§  71  FLUORIDES.  —  CHLOBIDES.  83 

with  silica,  is  heated  with  strong  sulphuric  acid,  fluoride  of 
silicon  is  evolved.  This  reaction  is  available  as  a  test  for 
fluorine. 

A  mixture  of  the  supposed  fluoride  and  fine  dry  sand  is 
heated  in  a  short,  dry  test-tube  with  concentrated  sulphuric 
acid.  A  drop  of  water,  caught  in  the  loop  of  a  clean  plati- 
num wire,  is  held  in  the  mouth  of  the  test-tube.  This  drop 
of  water  becomes  merely  dim,  quite  opaque,  or  almost  solid 
with  silicic  acid,  according  to  the  quantity  of  fluoride  of 
silicon  evolved  from  the  mixture.  The  gaseous  fluoride  of 
silicon  shows  white  fumes  when  it  comes  in  contact  with  moist 
air.  If  a  considerable  quantity  of  fluoride  of  silicon  be 
evolved  from  the  mixture  tested,  it  can  be  decanted  into 
another  test-tube,  and  there  shaken  up  with  water.  If  the 
substance  to  be  tested  for  fluorine  is  known  to  contain  silica, 
it  is,  of  course,  unnecessary  to  add  sand  to  it.  This  method 
applies  to  all  fluorides  decomposable  by  hot  sulphuric  acid. 
It  is  evident  that  this  test  reversed  can  be  applied  to  the  de- 
tection of  silica. 

Fluoride  of  calcium  (fluor-spar)  is  a  good  material  from 
which  to  obtain  these  two  tests  for  fluorine. 

71.  Chlorides.  —  The  following  confirmatory  test  is  ap- 
plied to  chlorides  in  the  dry  state. 

When  a  chloride,  in  powder,  is  heated  in  a  test-tube  with 
black  oxide  of  manganese  and  strong  sulphuric  acid,  chlorine 
gas  is  evolved  ;  this  gas  is  recognized  by  its  odor,  greenish- 
yellow  color,  and  reaction  with  iodo-starch  paper.  The  gas 
evolved  by  a  chloride  gives  no  colored  reaction  with  starch 
alone  ;  but  when  a  moistened  slip  of  paper,  on  which  a  mix- 
ture of  starch  paste  and  iodide  of  potassium  (App.,  §  38) 
has  been  spread,  is  held  in  an  atmosphere  or  current  of  chlo- 
rine, the  paper  is  colored  blue  in  consequence  of  the  liberation 
of  iodine  which  the  chlorine  effects.  The  yellow  color  of  the 
gas  is  best  seen  by  looking  lengthwise  through  the  tube. 

It  is  often  difficult  to  obtain  black  oxide  of  manganese 
which  will  not  of  itself  give  a  reaction  for  chlorine  when 


84  BEOMIDES.  §  72 

treated  with  pure  sulphuric  acid.  Instead  of  this  reagent,  pyre 
bichromate  of  potassium  in  powder  may  be  employed.  The 
sulphuric  acid  used  should  be  diluted  with  an  equal  bulk  of 
water.  The  action  which  takes  place  is  similar,  except  that 
the  chlorine  is  accompanied  by  chlorochromic  acid  (CrClO2) 
which  in  part  condenses  as  a  yellow  liquid  on  the  sides  of  the 
tube.  The  reaction  on  iodo-starch  paper  is,  however,  obtained 
without  difficulty. 

Mercurous  chloride  (calomel)  gives  no  reaction  for  chlorine 
when  treated  with  binoxide  of  manganese  (or  bichromate  of 
potassium)  and  sulphuric  acid.  The  chlorine  may  be  de- 
tected, however,  by  treating  the  salt  in  powder  with  zinc  and 
dilute  sulphuric  acid.  The  mercury  is  reduced  to  the  metallic 
state  and  the  chlorine  goes  into  solution  as  chloride  of  zinc ; 
in  this  solution  the  chlorine  may  be  discovered  by  the  ordin- 
ary tests. 

72.  Bromides.  —  The  confirmatory  tests  for  bromides  de- 
pend upon  the  setting  free  of  bromine  itself. 

Hot  nitric  acid  liberates  the  bromine  from  all  bromides  ex- 
cept those  of  silver  and  mercury.  In  solutions,  the  free 
bromine  produces  a  yellow  coloration  ;  when  set  free  from 
solid  bromides  in  a  long  and  narrow  tube,  the  brownish-yel- 
low vapors  of  bromine  condense  into  a  liquid  upon  the  cold 
walls  of  the  tube. 

When  bromides,  in  powder,  are  heated  in  a  test-tube  with 
black  oxide  of  manganese  (or  bichromate  of  potassium)  and 
strong  sulphuric  acid,  brownish-red  vapors  of  bromine  are 
evolved.  If  chlorides  are  also  present,  the  bromine  will  be 
mixed  with  chlorine. 

To  identify  bromine  and  distinguish  it  from  chlorine,  moist- 
ened starch  is  brought  into  contact  with  the  free  bromine.  A 
yellow  or  orange^ellow  coloration  of  the  starch  marks  the 
presence  of  bromine.  To  apply  this  test,  thrust  a  rod  smeared 
with  starch-paste  into  the  tube  which  contains  the  bromine 
vapors ;  or,  when  greater  delicacy  is  requisite,  perform  the 
experiment  which  is  expected  to  liberate  bromine  in  a  very 


§§  73,  74  IODIDES.  -  NITRATES.  85 

small  beaker,  and  cover  this  beaker  with  a  watch-glass  to 
whose  under  side  is  attached  a  bit  of  paper  moistened  with 
starch  paste  and  sprinkled  with  dry  starch. 

Bromide  of  potassium  is  a  good  substance  with  which  to 
study  the  tests  for  bromine. 

''  73.  Iodides.  —  When  an  iodide,  in  the  solid  form  or  in 
solution,  is  heated  with  strong  nitric  acid,  iodine  is  liberated 
and  sublimes  in  violet  vapors. 

Free  iodine  in  vapor  is  recognized  by  the  deep  blue  color 
which  it  imparts  to  starch-paste.  Vapors  may  be  tested  by 
bringing  into  contact  with  them  a  glass  rod  smeared  with  thin 
starch-paste,  or  a  slip  of  white  paper  on  which  the  paste  has 
been  spread. 

The  best  method  of  detecting  iodine  in  a  solution  is  to  add 
a  few  drops  of  thin,  clear  starch-paste  to  the  liquid,  and  then 
set  free  the  iodine  by  means  of  nitrite  of  potassium  (App., 
§  37),  as  follows :  —  The  cold  fluid  to  be  tested  is  acidulated 
with  dilute  chlorhydric  or  sulphuric  acid,  after  the  addition 
of  the  starch-paste,  and  a  drop  or  two  of  a  concentrated  solu- 
tion of  nitrite  of  potassium  is  then  added.  A  dark  blue  color 
will  be  instantly  produced.  It  is  essential  that  the  liquid 
should  be  kept  cool,  for  the  blue  coloration  is  destroyed  by 
heat. 

Like  chlorine  and  bromine,  iodine  is  liberated  by  heating 
an  iodide  with  black  oxide  of  manganese  (or  with  bichromate 
of  potassium)  and  sulphuric  acid.  The  iodine  so  liberated 
is  readily  distinguished  by  the  above  tests. 

The  student  can  try  all  these  tests  for  iodine  with  a  small 
crystal  of  iodide  of  potassium. 

74.  Nitrates.  — •  The  preliminary  examination  generally 
gives  warning  of  the  presence  of  a  nitrate  :  to  confirm  the  pres- 
ence of  a  nitrate,  one  or  both  of  the  two  following  tests  may 
be  used :  — 

If  the  solution  of  a  nitrate  is  mixed  with  an  equal  volume 
of  strong  sulphuric  acid,  the  mixture  cooled  in  cold  water, 
and  a  concentrated  solution  of  ferrous  sulphate  then  cautiously 

8 


86  NITRATES.  -  CHLORATES.  §  75 

added  to  it  in  such  a  way  that  the  two  fluids  do  not  mix,  the 
stratum  of  contact  shows  a  purple  or  reddish  color,  which 
changes  to  a  brown.  If  the  fluids  are  then  mixed,  a  clear 
brownish-purple  liquid  is  obtained.  The  color  fades  on  heat- 
ing. Another  way  of  performing  the  same  test  is  to  drop  a 
crystal  of  copperas  into  the  cold  mixture  of  nitrate  and  sul- 
phuric acid.  There  forms  around  the  crystal  a  dark  halo, 
which  disappears  with  a  kind  of  effervescence  on  the  appli- 
cation of  heat.  It  is,  of  course,  essential  that  the  sulphuric 
acid  employed  for  this  test  should  be  so  free  from  nitric 
and  hyponitric  acids,  as  not  itself  to  give  this  reaction  with 
ferrous  sulphate. 

Boil  some  chlorhydric  acid  in  a  test-tube,  add  to  it  one  or 
two  drops  of  a  dilute  solution  of  sulphindigotic  acid  (App., 
§  57),  and  continue  the  boiling  a  moment.  If  the  chlorhy- 
dric acid  is  sufficiently  free  from  chlorine,  the  resulting  liquid 
*Will  be  of  a  faint  blue  color.  If  a  nitrate,  either  solid  or  in 
solution,  be  added  to  this  liquid  and  the  mixture  be  again 
boiled,  the  liquid  will  be  decolorized.  This  reaction  is  deli- 
cate ;  but  there  are  some  other  substances,  especially  free 
chlorine,  which  have  a  like  bleaching  effect. 

Nitrate  of  potassium  is  a  suitable  material  on  which  to 
illustrate  the  tests  for  nitrates. 

75.  Chlorates.  —  The  preliminary  examination  gives 
warning  of  the  presence  of  chlorates. 

When  a  few  particles  of  a  chlorate  in  the  solid  form  are 
covered  with  two  or  three  times  as  much  strong  sulphuric 
acid,  and  the  mixture  is  gently  warmed,  the  liquid  becomes 
intensely  yellow,  and  a  greenish-yellow  irritating  gas  of  pecu- 
liar odor  (hypochloric  acid,  CIO2)  is  evolved,  which  explodes 
with  violence  at  a  moderate  heat.  After  thisy  decomposition, 
the  gas  evolved  has  the  characteristic  odor  of  chlorine.  The 
quantity  of  chlorate  operated  upon  should  be  very  small. 

The  solution  of  a  chlorate  decolorizes  indigo-solution  pre- 
cisely like  the  solution  of  a  nitrate,  under  like  conditions 
(«  74). 


§  76  ACETATES.  87 

A  chlorate  is  converted  by  ignition  into  a  chloride,  from  a 
solution  of  which  nitrate  of  silver  precipitates  the  chlorine. 

Chlorate  of  potassium  illustrates  very  well  the  reactions  of 
chlorates. 

^76.  Acetates. — When  acetates  are  moderately  heated 
with  strong  sulphuric  acid,  hydrated  acetic  acid  distils  from  the 
mixture,  and  may  be  recognized  by  its  pungent  odor. 

When  an  acetate  is  heated  with  alcohol  and  sulphuric  acid 
in  equal  volumes,  acetic  ether  is  formed.  The  agreeable  odor 
of  this  ether  is  highly  characteristic. 

Hot  concentrated  sulphuric  acid  produces  no  blackening 
with  an  acetate. 

When  a  few  drops  of  a  solution  of  ferric  chloride  (A pp., 
§  48),  are  added  to  a  solution  of  a  neutral  acetate,  or  to  a 
solution  of  an  acetate  previously  neutralized  with  ammonia, 
the  liquid  acquires  a  dark  red  color,  because  of  the  formation 
of  ferric  acetate.  If  the  liquid  contain  an  excess  of  the  ace- 
tate, a  basic  acetate  of  iron  is  precipitated  in  yellow  flocks 
upon  boiling,  and  the  fluid  finally  becomes  colorless. 

Acetate  of  sodium  may  be  used  to  show  these  reactions  of 
the  acetates. 


PART  SECOND. 


THE    ACTUAL    EXAMINATION    OP    SUBSTANCES    OF   UN- 
KNOWN COMPOSITION. 

77.  The  substance  to  be  examined  may  be  either  solid  or 
liquid.  We  shall  consider  first  the  treatment  of  a  solid; 
afterwards  that  of  a  liquid.  The  solid  may  be  a  metallic 
substance,  that  is,  a  pure  metal  or  an  alloy,  or  it  may  be  a 
salt,  mineral,  or  other  non-metallic  body.  The  method  of 
procedure  differs  in  the  two  cases.  We  shall  describe  first 
the  treatment  of  a  salt,  mineral,  or  other  non-metallic  sub- 
stance. The  two  following  observations,  however,  apply  to 
all  cases.  The  student  should,  in  the  first  place,  learn  as 
much  as  possible  from  the  external  properties  of  the  substance 
to  be  analyzed,  from  its  color,  consistency  and  odor,  if  it  is  a 
liquid ;  from  its  color,  texture,  odor,  lustre,  hardness,  gravity 
and  crystalline  or  amorphous  structure,  if  it  is  a  solid.  By 
attentively  observing  the  characteristics  or  individual  peculi- 
arities of  every  substance  which  passes  through  his  hands, 
the  student  will  soon  learn  to  recognize  many  substances  at 
sight,  —  by  far  the  quickest  and  easiest  way  of  identifying 
them.  Secondly,  since  the  original  substance  must  be  several 
times  reverted  to  in  order  to  complete  an  analysis,  the  student 
should  husband  his  stock  of  the  substance  to  be  analyzed, 
never  employing  the.  whole  of  it  for  any  single  course  of  ex- 
periment. It  is  well  also  to  reserve  a  portion  for  unforeseen 
contingencies. 


90  CLOSED-TUBE  TEST.  §§  78-80 


CHAPTER   XI. 

TREATMENT   OF   A  SALT,   MINERAL,  OR  OTHER  NON- 
METALLIC  SOLID. 

ORDER  OF  PROCEDURE. 

78.  THE  general  course  pursued  in  the  analysis  of  a  non- 
metallic  solid  substance  consists,  as  a  rule,  in :  —  1st.    The 
preliminary  examination,  to  be  presently  described  ;  2d.     The 
bringing  the  substance  into  solution  ;  3d.     The  examination 
of  the  solution  obtained  for  the  metallic  elements  according 
to  the  methods  laid  down  in  Part  I,  Chaps  I- VIII ;  4th. 
The   application  of  such  general  and   special  tests  for  the 
non-metallic  elements  as  may  not  have  been  rendered  un- 
necessary by  facts  observed  during  the  preceding  course  of 
the  analysis. 

A.      PRELIMINARY   EXAMINATION   IN   THE   DRY  WAY. 

79.  The  preliminary  examination  in  the  dry  way  consists 
essentially  of  two  operations  ;  the  substance  is  first  subjected 
to  the  influence  of  heat  alone   (closed-tube  test,  §  80)  ;  and 
afterwards  a  second  portion  of  the  substance,  or,  in  some 
cases,  the  same  portion,  is  exposed  to  the  influence  of  heat 
and  certain  reducing  agents  (reduction  test,  §  81). 

80.  Closed-Tube  Test.  —  Prepare   a  hard   glass   tube 
No.  4  (App.,  §  £2),  about  three  inches  long,  and  closed  at 
one  end.     Let  fall  into  this  tube  a  minute  fragment  of  the 
solid,  or  a  little  of  its  powder.     If  the  substance  be  used  in 
powder,  wipe  out  the  tube  with  a  tuft  of  cotton  on  a  wire,  in 
order  that  the  interior  walls  of  the  tube  may  be  clean  to 
receive  a  sublimate.     Heat  the  substance  at  the  end  of  the 
tube,  at  first  gently  in  the  lamp,  but  finally  intensely  at  the 


§  80  CLOSED-TUBE  TEST.  91 

highest  temperature  to  be  obtained  with  the  Bunsen  gas- 
lamp,  or  in  the  blowpipe  flame.  The  following  are  the  most 
noteworthy  reactions  with  the  inferences  to  be  drawn  from 
them ;  it  not  unfrequently  happens  that  a  single  substance 
gives  several  of  these  reactions. 

I.  The  substance  blackens,  and  gases  or  vapors  are  evolved. 
These  vapors  often  have  a  disagreeable  smell,  sometimes  like 
that  of  burnt    sugar,  paper,  or  feathers.      Sometimes  they 
condense  in  tarry  droplets  ;  water  also  condenses  on'  the  cold 
part  of  the  tube.     These  appearances  indicate  the  presence 
of  organic  substances. 

Now  the  presence  of  fixed  organic  matter  interferes  with 
the  detection  of  many  substances,  and  it  must  be  destroyed 
before  the  analysis  can  be  proceeded  with.  The  method 
employed  to  this  end  is  detailed  on  page  97 ;  no  matter 
whether  the  substance  contain  organic  matter  or  not,  the 
closed-tube  test  is  immediately  succeeded  by  the  reduction  test. 

Simple  blackening  is  not  proof  of  the  presence  of  organic 
bodies.  Some  salts  of  copper  and  cobalt,  for  example, 
blacken  through  the  formation  of  a  black  oxide. 

When  organic  matter  is  shown  to  be  present,  the  student 
should  look  particularly,  at  the  proper  stage  of  the  analysis, 
for  acetates  (§  76)  and  tartrates  (§  67)  acids;  but  he  will 
not  forget  that  there  are  hundreds  of  organic  compounds 
which  are  not  comprehended  in  the  plan  of  this  treatise. 

II.  Tlie  substance  is  not  carbonized ,  but  vapors  or  gases 
escape  from  it.     The  most  important  are  :  — 

a.  Aqueous  vapo  •-,  which  condenses  in  the  upper  part  of 
the  tube.     Test  this  water  with  litmus  paper ;  if  it  is  alka- 
line, ammonia  may  be  suspected ;  if  acid,  some  volatile  acid 
(H2S04,  HC1,  HBr,  HI,  HP1,  HNO3,  etc). 

b.  Oxygen  recognized  by  its  relighting  a  glowing  match. 
This  gas  indicates  nitrates,  chlorates  and  peroxides.     If  the 
heated  substance  fuses,  and  a  small  fragment  of  charcoal 
thrown  in  is  energetically  consumed,  the  presence  of  a  nitrate 
or  chlorate  may  be  assumed. 


92  CLOSED-TUBE  TEST.  §  80 

c.  Hyponitric  acid,  recognized  by  the  brownish-red  color 
of  the  fumes.     It  results  from  the  decomposition  of  nitrates. 

d.  Sulphurous  acid^  recognized  by  its  odor.     It  not  un- 
frequently  results  from  the  decomposition  of  sulphates,  sul- 
phites and  sulphides. 

e.  Carbonic  acid,  derived  from  decomposable  carbonates, 
and  to  be  recognized  by  lime-water  (§  57). 

/.  Cyanogen,  derived  from  decomposable  cyanides,  and  to 
be  recognized  by  its  odor,  and  by  the  blue  flame  with  which 
it  burns  when  there  is  enough  of  it  to  be  lighted. 

g.  Sulphuretted  hydrogen,  derived  from  moist  sulphides, 
and  to  be  known  by  its  smell. 

h.  Ammonia,  resulting  sometimes  from  the  decomposition 
of  ammoniacal  salts. 

III.  A  sublimate  forms  beyond  the  heated  portion  of  the 
tube.  The  whole  of  the  substance  may  volatilize.  The  fol- 
lowing are  the  commonest  sublimates  :  — 

a.  Sulphur,  which  sublimes  in  reddish  drops.    The  sub- 
limate becomes   solid  and  yellow,  or  yellowish-brown,  on 
cooling. 

b.  Ammonium  salts  give  white  sublimates. 

Test  a  separate  small  portion  of  the  original  substance  for 
the  salts  of  ammonium,  by  mixing  it  in  a  small  test-tube  with 
an  equal  bulk  of  slaked  lime  and  a  few  drops  of  water,  and 
heating  the  mixture.  Ammonia,  when  evolved,  may  be  rec- 
ognized by  its  smell,  and  by  the  white  fume  produced  when 
a  rod  moistened  with  a  mixture  of  equal  parts  of  strong 
chlorhydric  acid  and  water  is  held  above  the  mouth  of  the 
tube.  Unless  the  original  solid  is  obviously  inalterable  by 
heat,  it  should  be  invariably  tested  in  this  way  for  ammonium 
salts. 

c.  Metallic  mercury  and  some  of  its  compounds.     The 
metal  sublimes  in  metallic  droplets.     The  two  chlorides  of 
mercury  give  sublimates  which  are  white  when  cold.     The 
red  iodide  of  mercury  gives  a  yellow  sublimate.     The  sul- 
phide of  mercury  gives  a  dull  black  sublimate. 


§  80  CLOSED-TUBE  TEST.  93 

d.  Arsenic  and  some  of  Us  compounds.     Metallic  arsenic 
gives  a  black  sublimate  of  metallic  lustre.     Arsenious  acid 
gives  a  white  sublimate  which  looks  crystalline  under  a  mag- 
nifying lens.     The  sulphides  of  arsenic  give  sublimates  which 
are  brownish-red  while  hot,  but  reddish-yellow  to  red  when 
cold  ;  these  sublimates  look  not  unlike  that  of  pure  sulphur. 

e.  Teroxide  of  antimony  first  fuses  to  a  yellow  liquid  and 
then  give  a  white  sublimate,  composed  of  needle-like  crystals. 

/.  Oxalic  acid  gives  a  white,  crystalline  sublimate  with 
dense  fumes  in  the  tube. 

Other  reactions  besides  those  just  mentioned  sometimes 
occur  during  the  examination  of  a  substance  in  the  closed- 
tubje :  they  are,  however,  of  less  importance  and,  in  fact,  the 
inferences  to  be  drawn  from  the  appearances  already  indi- 
cated are  of  very  unequal  value.  Thus  the  detection  of 
organic  matter  is  of  the  first  importance,  because,  as  has 
been  stated,  such  matters  must  be  got  rid  cf  before  the 
analysis  can  be  proceeded  with.  Again  the  presence,  or  en- 
tire absence,  of  ammonium  salts  should  be  put  beyond  doubt 
at  this  first  stage  of  the  examination.  Thirdly,  the  presence 
of  mercury,  or  of  mercurous  salts,  determines  the  choice  of 
the  acid  solvent  in  favor  of  nitric  acid,  in  case  water  will  not 
dissolve  the  substance  under  examination  (§  85),  and  the 
presence  of  mercuric  salts  renders  necessary  the  substitution 
of  sulphydrate  of  ammonium  for  sulphydrate  of  sodium  as 
the  solvent  for  the  sulphides  of  Class  III  (§  27).  Accord- 
ingly, it  is  useful  to  get  information  of  the  presence  of  mer- 
cury or  its  compounds  at  this  early  stage  of  the  examination. 
As  to  the  other  appearances,  they  give  information  which  may 
be  convenient,  but  is  never  essential  for  the  safe  conduct  of 
the  regular  course  of  analysis.  Practically  the  closed-tube 
test  may  generally  be  conducted  as  follows :  — 

The  substance  is  introduced  into  the  tube  as  stated  above, 
a  strip  of  moistened  litmus  paper  is  folded  loosely  across  the 
mouth  of  the  tube,  and  the  tube  heated  in  the  lamp,  at  first 
very  gently.  The  deportment  of  the  substance  is  observed 


94  SEDUCTION  TEST.  §  gl 

under  the  gentle  heat  at  first  applied  and  also  as  the  heat 
increases,  the  appearance  of  condensed  moisture  or  of  other 
sublimate  is  looked  for,  and  any  action  of  escaping  vapors 
on  the  litmus  paper  is  noted.  Meanwhile  the  tube  is  occa- 
sionally removed  from  the  lamp,  to  see  whether  any  peculiar 
odor  of  escaping  gas  may  be  detected.  Finally  any  water 
which  may  have  condensed  in  the  tube  is  tested  with  litmus 
paper.  The  student  should  note  any  other  appearances, 
whether  mentioned  above  or  not,  which  manifest  themselves 
during  the  examination,  as  they  may  serve  as  corroborative 
tests  when  the  composition  of  the  substance  has  finally  been 
made  out  with  some  certainty. 

81.  Reduction  Test.  —  Mix  a  little  of  the  powder  of.  the 
substance  under  examination  (the  bulk  of  a  hemp-seed)  with 
an  equal  quantity  of  carbonate  of  sodium,  and  make  the  mix- 
ture into  a  pasty  ball  with  a  small  drop  of  water.  Select  a 
piece  of  dry,  well  burned,  soft-wood  charcoal,  and  cut  out  of 
it  a  rectangular  block  about  6  inches  long,  1 J  in.  wide,  and  J 
to  5  in.  thick,  having  its  flat,  smooth  surface  (6  in.  by  1J  in.) 
at  right  angles  to  the  rings  of  growth  in  the  tree.  It  is  this 
surface  which  is  always  to  be  used.  A  good  piece  of  char- 
coal may  be  made  to  serve  for  many  assays  by  filing  off  the 
used  surface  and  exposing  a  new  one,  but  ordinary  charcoal 
allows  portions  of  the  flux  or  even  small  metallic  globules  to 
run  into  its  pores  or  into"  cracks  opened  by  the  heat,  and  can 
rarely  be  used  with  advantage  the  second  time.  At  a  quarter 
to  half  an  inch  from  the  end  of  the  piece  of  charcoal,  scoop 
out  with  a  penknife  a  little  cavity  of  the  size  of  half  a  pea. 
Place  the  prepared  pellet  in  this  cavity,  and  expose  it  for 
several  consecutive  minutes  to  the  reducing  flame  of  the 
blowpipe  (App.,  §  78). 

Under  these  conditions,  vapors  of  characteristic  odor  or 
appearance  may  be  evolved  ;  some  of  them  will  be  mentioned 
below.  The  two  objects,  however,  to  which  attention  is  spe- 
cially to  be  directed,  are  the  residue  in  the  cavity,  and  the 
incrustation  on  the  charcoal  outside  of  the  cavity. 


§  81  REDUCTION  TEST.  95 

The  following  metals  may  be  found  as  fused  metallic  glob- 
ules in  the  cavity ;  lead,  silver  and  gold  are  reduced  with 
ease,  even  by  an  inexperienced  operator ;  tin  and  copper  with 
some  difficulty :  — 

a.  Gold  —  a  yellow,  malleable  globule,  produced  without 

*  incrustation. 

b.  Copper  —  a  red,  malleable  globule,  produced  without 

incrustation. 

c.  Tin  —  a  bright,  white,  malleable  globule.     An  incrus- 

tation is  simultaneously  produced,  which  is 
faint  yellow  when  hot  and  white  when  cold  ; 
it  immediately  surrounds  the  globule. 

d.  Lead  —  a  very  fusible  and  very  malleable  globule.     A 

yellow  incrustation  is  simultaneously  pro- 
duced. 

e.  Silver  —  a  brilliant,  white,  malleable  globule,  produced 

without  incrustation. 

Two  other  common  metals,  bismuth  and  antimony,  may  be 
reduced  to  gray  metallic  globules,  but  these  globules  are 
brittle,  and  are  not  liable  to  be  confounded  with  the  malleable 
globules  just  described.  Bismuth  gives  a  yellow  incrustation 
which  resembles  that  of  lead. 

Common  charcoal  is  itself  very  apt  to  show  a  grayish  in- 
crustation of  ash  round  about  the  heated  assay  ;  this  incrus- 
tation remains  unaltered  or  increases,  when  directly  exposed 
to  the  flame.  The  student  should  test  each  piece  of  charcoal 
before  the  blowpipe  flame,  in  order  that  he  may  not  imagine 
a  deposit  of  ash  to  be  an  incrustation  derived  from  the  sub- 
stance under  examination. 

If  a  distinct  globule  has  been  obtained,  it  must  be  picked 
out  with  a  pair  of  jewellers'  tweezers,  and  pounded  on  some 
smooth  and  hard  body  to  test  its  malleability.  If  it  is  mal- 
leable, replace  it  upon  the  charcoal  at  an  unused  spot,  and 
heat  it  strongly  with  the  oxidizing  flame.  Gold  and  silver 
globules  fuse,  but  maintain  their  brilliancy  and  give  no  in- 


96  REDUCTION  TEST.  §  81 

crustation ;  this  proof  distinguishes  a  genuine  gold  globule 
from  a  yellow  globule  composed  of  an  alloy  of  copper  and 
some  white  metal.  A  yellow  globule  composed  of  oxidizable 
metals  tarnishes  instantly  in  the  oxidizing  flame.  A  tin 
globule  fuses,  but  its  bright  surface  is  instantly  tarnished , 
and  a  white  incrustation  of  binoxide  of  tin  is  produced 
which  cannot  be  driven  off  by  either  flame.  A  lead  globule 
is  rapidly  converted  into  litharge,  a  j^ellow  incrustation  being 
produced,  which  volatilizes  with  a  bluish  color  when  touched 
wit-h  the  reducing  flame.  A  copper  globule  is  blackened  by 
the  formation  of  oxide  of  copper,  and  the  blowpipe  flame  is 
tinged  with  green. 

Certain  other  phenomena  may  manifest  themselves  during 
this  experiment  for  the  reduction  of  malleable  metallic  glob- 
ules. Sulphur,  ammonium  salts  in  general,  the  chlorides, 
bromides,  iodides  and  sulphides  of  sodium  and  potassium, 
the  chlorides  of  lead,  bismuth,  tin  and  copper,  metallic  mer- 
cury, arsenic,  antimony  and  zinc,  and  many  compounds  of 
these  four  elements,  are  liable  to  pass  off  in  vapors,  which 
are  often  in  part  deposited  upon  the  coal  at  a  greater  or  less 
distance  from  the  hot  assay  according  to  their  volatility. 
With  the  exception  of  sulphur,  these  sublimates  are  white, 
but  when  deposited  in  a  thin  film  upon  the  black  coal  they 
have  a  gray  or  blue  appearance.  During  the  production  of 
the  arsenic  sublimate  a  peculiar  odor  is  evolved ;  this  sub- 
limate being  very  volatile  is  only  deposited  at  a  considerable 
distance  from  the  assay.  The  incrustation  produced  b}-  zinc 
is  distinctly  yellow  while  hot,  but  turns  white  on  cooling  ;  it 
settles  near  the  assay  and  is  driven  away  again  with  diffi- 
culty. Nitrates  and  chlorates  generally  give  warning  of  their 
presence  when  heated  on  charcoal  by  causing  deflagration. 

These  phenomena,  with  the  exception  of  the  reaction  of 
the  nitrates  and  chlorates,  are  of  secondary  importance  ;  the 
main  object  of  the  experiment  is  the  reduction  of  the  five 
malleable  metals  above  enumerated.  We  may  thus  obtain 
knowledge  of  the  presence  of  gold  (for  a  confirmatory  test, 


§  82  DESTROYING   ORGANIC  MATTER.  97 

see  §  96,  &.),  a  metal  not  included  in  our  scheme  of  analysis 
in  the  wet  way.  Tin  generally  gives  warning  of  its  pres- 
ence during  this  experiment ;  and  this  warning  is  of  use, 
because  it  is  inconvenient  to  apply  nitric  acid  as  a  solvent  to 
a  substance  containing  tin,  since  this  reagent  converts  tin 
into  the  very  insoluble  binoxide  of  tin.  The  detection  of 
copper  at  this  stage  is  of  little  advantage.  The  most  im- 
portant fact  deducible  from  the  reduction  test  is  the  presence 
of  either  silver  or  lead.  In  dissolving  an  unknown  sub- 
stance which  proves  to  be  insoluble  in  water,  it  is  customary 
to  try,  as  the  second  solvent,  chlorhydric  acid.  The  chlor- 
ides of  silver  and  lead  being  insoluble,  or  difficultly  soluble, 
this  acid  should  not  be  used  as  a  solvent  when  either  of  these 
two  metals  is  present.  Nitric  acid  must  be  used  instead. 
Moreover,  if  the  substance  has  already  given  evidence  of  the 
presence  of  organic  matter  (§  80),  porcelain,  and  not  pla- 
tinum, must  be  used  as  a  support  in  destroying  the  organic 
matter,  as  described  in  the  next  section,  whenever  an  easily 
reducible  metal  is  present. 

82.  Destruction  of  the  Organic  Matter,  —  As  already 
stated  in  §  80,  the  presence  of  fixed  organic  matter  interferes 
with  the  detection  of  many  substances,  and  it  must  be  de- 
stroyed before  the  analysis  can  be  proceeded  with.  A  por- 
tion of  the  original  substance,  sufficient  for  the  regular  course 
of  examination  for  the  metallic  elements,  is  ignited  in  a  por- 
celain crucible,  with  free  access  of  air,  or  better,  on  platinum 
foil,  if  the  absence  of  any  easily  reducible  metal  has  been 
proved  by  the  reduction  test,  until  all  the  carbon  is  burnt  out 
of  it.  This  ignition  is  best  performed  on  successive  small 
portions  rather  than  on  a  large  mass  at  once. 

It  is  obvious  that  some  inorganic  volatile  matters  may  be ' 
lost  during  this  ignition.  Furthermore,  some  substances, 
especialty  alumina  and  chromic  and  ferric  oxides,  are  made 
very  insoluble  by  ignition.  Exceptionally,  therefore,  the  fol- 
lowing process,  which  is  not  liable  to  these  objections,  is 
employed  :  —  The  substance  in  powder,  paste  or  concentrated 
9 


98  SOLUTION.  §  83 

solution,  is  heated  in  an  evaporating-clish,  with  strong  nitric 
add,  to  a  temperature  just  below  boiling.  To  this  hot  mix- 
ture chlorate  of  potassium,  in  small  bits,  is  added  gradually 
during  several  minutes  or  until  the  organic  matter  is  all 
destroyed.  The  solution  is  then  evaporated  to  dryness  on  a 
water-bath ;  the  dry  residue  is  moistened  with  strong  chlor- 
hydric  acid,  the  mixture  diluted  with  water,  warmed,  and 
filtered,  if  there  be  any  residue.  The  filtrate  is  fit  for  the 
regular  course  of  analysis,  except  that  potassium,  having 
been  added,  must  not  be  tested  for  in  this  liquid.  The  res- 
idue, if  any,  must  be  examined  for  the  insoluble  chlorides  of 
Class  I.  This  process  is  simply  a  combustion  at  a  low  tem- 
perature. 

The  only  classes  of  salts,  coming  within  the  scope  of  this 
manual,  which  in  the  closed  tube  give  evidence  of  the  pres- 
ence of  organic  matter,  are  the  acetates  and  tartrates.  It 
will,  of  course,  be  necessary  to  apply  the  tests  for  acetic  and 
tartaric  acid  to  a  portion  of  the  original  substance  and  not 
to  the  solution  obtained  above.  But  the  student  will  not  for- 
get that  the  statement  already  made  in  §  80,  that  the  presence 
of  organic  matter  does  not  necessarily  imply  the  presence  of 
either  acetates  or  tartrates. 

B.       DISSOLVING   A    SALT,    MINERAL,    OR     OTHER     NON-METALLIC 
SOLID,    FREE    FROM   ORGANIC   MATTER. 

83.  Before  a  solid  substance  can  be  submitted  to  the 
systematic  course  of  analysis,  it  must  be  brought  into  solu- 
tion. There  is  no  universal  solvent.  Different  substances 
require  different  solvents.  The  four  solvents  employed  in 
qualitative  analysis  for  salts,  minerals,  and  other  non-metallic 
solids,  are  water,  chlorhydric  acid,  nitric  acid  and  aqua 
regia ;  and  these  four  liquids  are  to  be  tried  in  the  precise 
order  in  which  they  here  stand.  Water  is  always  to  be  tried 
first ;  to  whatever  resists  water,  strong  chlorhydric  acid  is 
applied ;  if  chlorhydric  acid  fails  to  dissolve  the  solid  com- 
pletely, nitric  acid  is  tried,  and  after  nitric  acid,  aqua  regia 


§§84,85  SOLUTION.  99 

as  the  last  resort.  If  for  reasons  stated  in  §  81,  the  prelimi- 
nary examination  has  shown  chlorhydric  acid  to  be  unsuitable 
as  a  solvent,  nitric  acid  is  tried  immediately  after  water,  and 
lastly  aqua  regia  as  before.  A  solid  substance  should  in- 
variably be  reduced  to  a  very  fine  powder,  before  being  sub- 
mitted to  the  action  of  solvents  (App.,  §  91). 

84.  Dissolving  in  Water.  —  About  half  a  thimbleful  of 
the  powdered  substance  is  boiled  with  ten  times  as  much 
water  in  a  test-tube.  If  an  effervescence  occurs,  as  is  possi- 
ble with  mixtures  containing  an  acid  salt  (yeast-powders,  for 
example),  the  gas  evolved  should  be  carefully  tested  (§  56- 
61).  If  the  substance  dissolves  completely,  the  solution  is 
ready  for  analysis.  When  undissolved  powder  remains  in 
the  tube  after  protracted  boiling,  filter  a  few  drops  of  the 
liquid,  and  evaporate  a  drop  or  two  of  the  filtrate  to  dry  ness 
on  clean  platinum  foil,  at  as  low  a  heat  as  possible.  If  there 
be  no  residue  on  the  foil,  or  if  the  residue  be  scarcely  appre- 
ciable, the  substance  is  practically  insoluble  in  water,  and 
acids  must  be  tried  as  solvents.  But  if,  on  the  contraiy,  a 
tolerable  residue  remains  on  the  foil,  decant  the  liquid  in  the 
tube  into  the  filter,  and  boil  the  powder  again  with  water. 
Persevere  with  this  treatment  until  it  is  evident  that  a  part 
of  the  powder  is  insoluble  in  water.  The  insoluble  residue 
in  the  test-tube  is  filtered  off;  the  clear  filtrates,  collected 
together  and  concentrated  by  evaporation  if  of  unreasonable 
bulk,  are  to  be  labelled  "  H2O  Sol."  and  reserved  for  the 
regular  course  of  analysis  (§86).  In  this  case,  and  in  the 
still  more  favorable  case  in  which  all  the  substance  has  dis- 
solved in  water,  it  is  a  simple  aqueous  solution  which  is  sub- 
mitted to  analysis. 

85  Dissolving  in  Acids.  —  The  substance  which  water 
has  failed  to  dissolve,  either  in  whole  or  in  part,  is  next  boiled 
in  a  small  dish  with  three  or  four  times  its  bulk  of  concen- 
trated chlorhydric  acid,  unless  the  tube  test  (§  80)  or  the  re- 
duction test  (§81)  has  proved  the  presence  of  silver,  lead  or 
mercury :  in  which  case  nitric  acid  is  the  first  acid  to  be  tried. 


100  SOLUTION.  §  85 

(See  the  next  paragraph  )  If  an  effervescence  occur,  the 
escaping  gas  is  to  be  tested,  as  described  in  §§  56-61.  After 
boiling  the  powdered  substance  with  the  strong  acid,  dilute 
the  fluid  with  twice  its  bulk  of  water,  and  repeat  the  boiling 
if  any  residue  remain  undissolved.  The  acid  is  diluted  be- 
cause, though  the  substance  to  be  dissolved  is  best  attacked 
in  the  first  instance  by  strong  acid,  the  salts  formed  by  the 
action  of  the  concentrated  acid  are  more  likely  to  dissolve* 
readily  in  a  dilute  than  in  a  strongly  acid  liquor.  Not  a  few 
salts  which  scarcely  dissolve  in  strong  acids,  are  readily  solu- 
ble in  the  same  acids  when  diluted.  If  the.  whole  of  the 
substance  finally  dissolves,  the  solution  still  farther  diluted 
is  ready  for  the  transmission  of  sulphuretted  hydrogen  (§  24), 
for  it  is  of  course  unnecessary  to  examine  it  for  members  of 
Class  I.  If,  on  the  contrary,  an  undissolved  residue  remain 
in  the  tube,  ascertain  if  anything  has  dissolved,  by  carefully 
evaporating  two  or  three  drops  of  the  fluid  to  dryness  on 
platinum  foil.  Should  an  appreciable  residue,  in  excess  of 
that  given  by  two  or  three  drops  of  the  acid  employed,  re- 
main upon  the  foil,  separate  the  liquid  in  the  tube  from  the 
undissolved  substance  by  decantation  or  filtration.  Reserve 
the  solution,  labelling  it  "HC1  Sol." 

Rinse  the  undisolved  powder  with  water,  and  then  boil  it 
in  an  evaporating  dish  with  three  or  four  times  its  bulk  of 
strong  nitric  acid.  If  the  original  substance  contains  silver, 
lead  or  a  mercurous  salt,  chlorhydric  acid  will  not  have  been 
used,  and  it  will  be  the  residue  from  the  aqueous  solution, 
which  is  now  to  be  boiled  with  nitric  acid.  In  this  case, 
effervescence  is  to  be  watched  for.  If  the  substance  dissolves 
completely  in  the  strong  acid,  or  dissolves,  with  the  exception 
of  a  light  yellow  mass  of  sulphur,  which  often  separates  from 
a  sulphide,  evaporate  the  liquid  to  a  very  small  bulk  to  drive 
off  the  free  acid,  dilute  the  evaporated  solution  with  several 
times  its  bulk  of  water,  separate  the  sulphur,  if  necessary,  by 
filtration,  and  reserve  the  solution,  labelling  it  "HNO3  Sol." 
If  the  substance  does  not  completely  dissolve  in  the  strong 


§  85  SOLUTION. 

acid,  dilute  the  fluid  with  twice  its  bulk  of  water,  and  repeat 
the  boiling.  If  the  dilute  nitric  acid  effects  complete  solution, 
reserve  the  solution,  labelling  it  as  before,  u  HWO3  Sol."  If 
neither  the  strong  nor  the  diluted  nitric  acid  effects  the  com- 
plete solution  of  the  substance,  ascertain  if  anything  has  dis- 
soh^ed  in  the  dilute  acid  by  the  usual  test  on  platinum  foil. 
If  an  appreciable  residue  remain  on  the  foil,  separate  the 
undissolved  solid  in  the  dish  from  the  liquid  by  decantation 
or  filtration,  and  reserve  the  solution. 

Boil  the  powder,  which  has  resisted  both  acids  taken  singly, 
with  aqua  regia.  If  it  dissolves  completely,  evaporate  the 
solution  to  a  very  small  bulk,  dilute  the  evaporated  solution 
largely  with  water,  and  reserve  it  for  analysis,  labelling  it 
u  Aq.  Reg.  Sol."  It  is  useless  to  look  for  members  of  Class  I 
in  such  a  solution.  If,  on  the  contrary,  it  does  not  com- 
pletely dissolve  after  protracted  boiling,  test  the  liquor  to  see 
if  anything  has  dissolved.  If  an  appreciable  residue  remains 
on  the  foil,  dilute  the  acid  fluid,  filter  it,  reserve  the  solution 
labelled  as  before,  and  wash  the  undissolved  residue  thor- 
oughly with  water,  to  prepare  it  for  further  treatment  (§  86). 

Certain  silicates,  when  boiled  with  concentrated  acids,  are 
decomposed,  and  gelatinous  silicic  acid  is  separated.  This 
happens  but  rarely,  however,  in  the  rapid  processes  of  quali- 
tative analysis;  and  if  it  shoujd  happen,  it  is  not  likely  to 
lead  the  student  into  error.  A  residue  insoluble  in  all  acids 
will  remain ;  this  residue  is,  or  contains,  free  silicic  acid. 

It  must  not  be  supposed  that  it  is  common  to  try  all  four 
solvents  on  one  and  the  same  substance.  Water  and  chlor- 
hydric  acid  are  the  common  solvents ;  nitric  acid  and  aqua 
regia  are,  actually,  but  seldom  resorted  to  as  solvents,  except 
for  metals  (§  96).  It  would  require  some  ingenuity  to  devise 
an  artificial  mixture  which  would  put  to  the  test  all  the  capa- 
bilities of  the  above-described  method  of  bringing  solids  into 
solution  in  water  and  acids.  Such  mixtures  are  not  met  with 
in  ordinary  experience.  It  is  the  object  of  any  method  of 
analysis  to  meet  real  problems,  not  artificial  complications 
which  may  be  imagined  but  which  do  not  occur  in  fact. 


102  AX  AQUEOUS  SOLUTION.  §  86 

C.   TREATMENT  OF  THE  SOLUTIONS  OBTAINED. 

86.  Since  substances  which  prove  to  be  insoluble  in  water 
and  in  acids  must  be  brought  into  solution  by  peculiar 
methods,  we  proceed  to  consider  first  the  treatment  of  the 
solutions  already  obtained. 

I.  An  Aqueous  Solution.  —  If  the  student  is  assured  that 
the  unknown  substance  is  a  simple  salt,  he  may  draw  some 
trustworthy  inferences  from  the  fact  that  the  substance  dis- 
solves in  water.  Of  the  salts  which  fall  within  the  scope  of 
this  manual,  the  following  are  practically  soluble  in  water : 

1.  All  salts  of  sodium,  and  all  of  potassium  and  am- 

monium, except  tneir  double  platinum-chlorides. 

2.  All  nitrates,  chlorates  and  acetates. 

3.  Chlorides,  bromides  and  iodides,  except  those  of  silver 

and  mercury,  and  the  double  platinum-chlorides  of 
potassium  and  ammonium.  (Mercuric  chloride  is 
soluble.  The  lead  salts  are  difficultly  soluble). 

4.  Sulphates,   except  those   of   barium,  strontium'   and 

lead. 

5 .  Many  hyposulphites. 

6.  The  sulphides  of  sodium,  potassium,  ammonium,  mag- 

nesium, barium,  strontium  and  calcium. 

7.  A  few  cyanides,  oxalates,  tartrates  and  chromates,  be- 

sides those  of  the  alkali-metals  already  mentioned. 

It  is  obvious  that  any  element  of  the  thirty-six  considered 
in  this  treatise,  may  be  present  in  an  aqueous  solution  ;  but 
it  is  also  evident  from  the  above  list,  that  a  great  number  of 
salts  are  absolute^  excluded  because  of  their  insolubility  in 
water. 

If,  on  the  contrary,  there  is  no  certainty  that  the  substance 
under  examination  is  not  a  complex  artificial  mixture,  few 
conclusions  can  be  safely  drawn  from  the  fact  that  a  part  of 
it  or  the  whole  of  it  dissolves  in  water. 

Test  the  solution  with  litmus  paper.  The  solution  is  either 
neutral,  acid,  or  alkaline. 


§  86  AN  AQUEOUS  SOLUTION.  103 

a.  The  solution  is  neutral, —  The  normal  salts  of  most 
of  the  metals  have  an  acid  reaction.     Sodium,  potassium, 
barium,  strontium,  calcium,  magnesium,  manganese  and  silver, 
are  the  only  metallic  elements  which  form  salts  whose  solu- 
tions are  neutral.     Add  to  two  or  three  drops  of  the  solution 
a  drop  or  two  of  carbonate  of  sodium.     If   a   precipitate 
forms,  any  of  the  above  mentioned  elements  may  be  present, 
and  are  to  be  tested  for  in  regular  course  according  to  the 
methods  of  Part  I ;  if  no  precipitation  ensues,  only  sodium 
and  potassium  can  be  present,  and  they  may  be  tested  for 
directly,  as  described  in  Chap.  VIII. 

b.  The  solution  is  acid.  —  The  acidity  may  be  caused  by 
a  normal  salt  having  an  acid  reaction,  or  by  an  acid  salt. 
Neither  carbonates  nor  sulphides  can  be  present  in  an  aque- 
ous solution  with  an  acid  reaction.     The  solution  is  to  be 
tested  for  the  metallic  elements  in  the  usual  manner. 

c.  The  solution  is  alkaline.  —  The  alkalinity  may  be  due 
to  the  hydrates,  sulphides,  cyanides,  or  carbonates,  of  the 
metals  belonging  to  classes  VI  and  VII ;  to  the  presence  of  a 
borate,  silicate,  phosphate,  arseniate  or  aluminate  of  sodium 
or  potassium  ;  to  free  ammonia  or  to  carbonate  of  ammonium. 
If  the  alkalinity  proceed  from  an  alkaline  sulphide,  the  metals 
whose  sulphides  are  insoluble  in  water  and  in  alkaline  sul- 
phides, must  be  absent.     If  it  is  due  to  the  presence  of  the 
hydrates  or  carbonates  of  the  metals  of  classes  VI  and  VII,  a 
very  large  number  of  substances  a1  e  excluded.     If  it  proceed 
from  ammonia  or  carbonate  of  ammonium,  all  substances  pre- 
cipitable  by  these  reagents  are  absent. 

An  alkaline  solution  may  obviously  contain  some  substance, 
soluble  in  an  alkaline  solvent  like  caustic  soda  or  sulphydrate 
of  ammonium,  but  liable  to  immediate  precipitation  when  this 
solvent  is  destroyed  by  the  addition  of  chlorhydric  acid  at 
the  first  step  of  the  analysis.  Thus  any  sulphide  of  Class  III 
dissolved  in  caustic  soda  or  in  an  alkaline  sulphide,  or  com- 
pounds of  alkaline  hydrates  with  the  hydrates  of  aluminum, 
zinc  or  chromium,  would  be  precipitated  when  the  alkaline 


104  AN  AQUEOUS  SOLUTION.  §  86 

solvent  was  neutralized.  Again,  the  alkaline  solution  of  a 
silicate  of  sodium  or  potassium,  when  neutralized  with  acid, 
yields  a  very  gelatinous  whitish  precipitate  of  hydrated  silicic 
acid.  From  a  very  concentrated  solution  of  a  borate,  boracic 
acid  separates  in  colorless,  shining,  flat  crystals,  when  the 
solution  is  acidified  with  chlorhydric  acid ;  but  the  boracic 
acid  thus  separated  dissolves  when  the  solution  is  diluted. 
Again,  (although,  of  course,  this  could  not  happen  in  the 
case  of  an  alkaline  solution  actually  made  by  dissolving  a 
solid  substance  in  water)  chloride  of  silver  dissolved  in  am- 
monia-water would  be  thrown  down  by  any  acid  added  in 
excess. 

In  view  of  these  possibilities,  an  alkaline  aqueous  solution 
should  be  carefully  neutralized  with  nitric  acid,  as  a  prelimi- 
nary measure,  before- chlorhydric  acid  is  added  to  it.  Effer- 
vescence should  be  watched  for,  and,  if  it  occurs,  studied  as 
directed  in  §§  56-61.  Several  different  cases  of  precipitation 
may  be  distinguished,  requiring  somewhat  different  treat- 
ment. 

a.  If  the  characteristic  gelatinous  precipitate  of  silicic 
acid  appears,  the  acidulated  solution  must  be  evaporated  to 
dryness  and  ignited.  The  silicic  acid  is  thus  rendered  in- 
soluble. The  ignited  residue  is  digested  with  dilute  nitric 
acid  and  filtered.  The  filtrate  is  ready  for  the  usual  course 
of  analysis.  The  insoluble  residue  is  silicic  acid. 

I).  If  the  glistening,  colorless  plates  of  boracic  acid  ap- 
pear, dilution  with  warm  water  will  cause  them  to  redissolve. 

c.  If  a  precipitate  appear  on  neutralization,  whose  color 
or  texture  proves  that  it  is  neither  silicic  nor  boracic  acid, 
but  some  substance  insoluble  in  water  and  dilute  acids,  thrown 
down  in  consequence  of  the  destruction  of  its  alkaline  sol- 
vent, the  liquid  is  made  slightly  acid  and  then  filtered.  The 
filtrate  is  ready  for  the  usual  course  of  analysis.  The  pre- 
cipitate, rinsed  with  a  little  water,  is  reserved  for  further 
treatment ;  it  is  not  properly  a  substance  soluble  in  water, 
and  it  must  be  brought  into  solution  by  other  methods,  here- 


§§  86, 87  -^V  ACID  SOLUTION.  105 

after  to  be  described.  Sometimes  a  precipitate  forms  on 
exact  neutralization  of  an  alkaline  fluid,  which  redissolves 
when  the  acid  is  added  in  excess. 

II.  An  acid  solution.  —  Of  the  three  kinds  of  acid  solu- 
tions described  in  §  85,  any  one,  any  two,  or  all  three,  may 
be  obtained  from  a  single  mixture  of  different  solids.  There 
is  an  advantage  in  knowing  that  a  part  of  a  complex  mixture 
is  soluble  in  water,  a  part  in  chlorhydric  acid,  a  part  in  nitric 
acid  and  a  part  only  in  aqua  regia  ;  because  this  knowledge 
may  enable  the  student,  when  he  has  found  out  all  the  ele- 
ments of  the  mixture,  to  make  a  more  probable  guess  at  the 
manner  of  their  combination  in  the  original  mixture,  than  he 
would  otherwise  be  able  to.  But  it  is  quite  unnecessary  to 
keep  the  three  kinds  of  acid  solution  apart,  when  all  three 
have  been  obtained,  and  to  analyze  them  separately.  On  the 
contrary,  all  three  should  be  mixed  together,  and  analyzed  in 
one  course  of  testing.  It  must  only  be  borne  in  mind  that 
when  lead,  silver,  or  mercurous  salts  are  present,  the  nitric 
acid  solution  of  the  residue  from  the  aqueous  solution,  will 
give  a  precipitate  of  the  insoluble  chlorides  of  Class  I,  on 
being  mixed  with  a  chlorhydric  acid  or  aqua  regia  solution. 

The  student  must  be  careful  to  use  no  more  acid  than  is 
absolutely  essential.  Nitric  acid,  particularly,  is  very  objec- 
tionable ;  because  when  free  it  reacts  upon  sulphuretted 
hydrogen  with  mutual  decomposition,  sulphur  being  set  free. 
It  has,  therefore,  been  already  prescribed  to  remove  the 
greater  part  of  the  free  acid  by  evaporation.  Sometimes  a 
strongly  acid  solution  becomes  turbid  when  merely  diluted 
with  water.  This  phenomenon  points  to  the  presence  of  bis- 
muth or  antimony.  The  turbidity  will  disappear  again  on 
the  addition  of  chlorhydric  acid. 

The  mixed  acid  solutions,  after  the  filtration  from  any  pre- 
cipitated chlorides  of  Class  I,  as  first  mentioned,  are  submitted 
to  the  regular  course  of  analysis  for  the  metallic  elements. 

87.  Examination  of  the  Solutions  for  the  non-metal- 
lic Elements. —  As  has  been  already  stated  in  §45,  the 


106         TESTS  FOR  NON-METALLIC  ELEMENTS.         §  87 

examination  for  the  non-metallic  elements  invariably  follows 
'that  for  the  metallic  elements.  The  method  of  procedure  is 
usually  as  follows  :  If  the  substance  is  -soluble  in  water  and 
there  is  reason  to  believe  that  it  is  not  a  complex  artificial  mix- 
ture, but  a  simple  substance,  the  determination  of  the  metal- 
lic element  generally  proclaims  the  absence  of  certain  classes 
of  salts,  so  that  it  is  very  seldom  necessary  to  apply  more 
than  the  barium  and  the  silver  tests  and  a  few  special  tests. 
This  will  best  be  illustrated  by  taking  two  examples. 

Suppose  a  homogeneous  solid,  which  dissolves  readily  in 
water,  and  which  proves  to  contain  strontium.  Of  the  classes 
of  salts  coming  within  the  range  of  this  manual  (see  p.  65), 
only  the  sulphide,  chloride,  bromide,  iodide,  cyanide,  nitrate, 
chlorate  and  acetate  of  strontium  are  soluble  in  water ;  the 
presence  or  absence  of  a  sulphide  (and  probably  of  a  cyanide) 
will  have  been  shown  when  chlorhydric  acid  was  added  to 
precipitate  the  members  of  Class  I ;  the  silver  test  will  show 
either  the  presence  or  absence  of  the  chloride,  bromide, 
iodide  and  cyanide,  and  these  various  classes  of  salts,  if  any 
are  present,  must  be  distinguished  by  special  tests ;  special 
tests  must  also  be  applied  for  nitrates  and  chlorates  and  also 
for  acetates  if  the  substance  blackened  in  the  closed  tube. 
In  this  case,  then,  the  silver  test  is  the  only  general  t^st 
necessary,  and  the  number  of  special  tests  could  hardly  be 
more  than  four  or  five. 

Again,  suppose  the  substance  soluble  in  water  proves  to 
contain  a  mercurous  salt,  the  only  classes  of  salts  to  be  sought 
for  would  be  the  sulphate  (to  be  decided  by  the  barium  test) , 
the  cyanide,  chlorate,  nitrate  and  acetate  (to  be  determined 
by  special  test). 

If  the  only  metallic  element  found  in  an  aqueous  solution 
were  sodium  or  potassium  (or  the  radical  ammonium),  it 
would  be  necessary  to  look  for  all  the  classes  of  salts  enu- 
merated on  page  65.  In  this  case  the  barium  test  would  be 
applied  first,  then  the  silver  test,  then  such  special  tests  as 
had  not  been  rendered  unnecessary  by  negative  evidence 


§  87        TESTS  FOR  NON-METALLIC  ELEMENTS.         1Q7 

obtained  from  the  general  tests.  The  calcium  test  would  also 
be  applied  if  the  barium  test  had  made  the  presence  of  an 
oxalate,  tartrate  or  fluoride  not  impossible. 

In  the  case  of  an  acid  solution  the  conclusions  to  be  drawn 
from  the  presence  of  certain  metallic  elements  are  not  so  gen- 
eral, still  in  the  case  of  simple  substances  the  absence  of  cer- 
tain classes  of  salts  will  generally  be  made  sure.  For  example, 
a  substance  under  examination,  presumptively  a  simple  salt, 
proves  to  be  insoluble  in  water,  soluble  in  chlorhydric  acid 
and  to  contain  nickel.  The  sulphate,  chloride,  borate,  chro- 
mate,  bromide,  iodide,  chlorate,  acetate  and  nitrate  of  nickel 
are  soluble  in  water  and  for  this  reason  are  excluded  from 
consideration  ;  the  sulphite,  hyposulphite,  sulphide,  arseniate, 
arsenite  and  carbonate  would  have  revealed  themselves  in 
the  course  of  the  examination  for  the  metallic  elements,  and 
the  only  salts  to  be  specially  tested  for  at  this  point  are  the 
phosphate,  oxalate,  tartrate  and  silicate.  If  the  general  and 
special  tests  fail  to  indicate  the  presence  of  any  of  the  classes 
of  salts  mentioned  on  page  65,  the  substance  may  be  an 
oxide  or  hydrate.  The  hydrates  give  off  water  when  heated 
in  a  closed  tube  ;  peroxides  sometimes  give  off  oxygen  under 
the  same  conditions,  and  most  oxides  when  mixed  with  an 
excess  of  carbon,  and  heated,  give  off  carbonic  oxide,  or 
carbonic  acid ;  these  gases  may  be  recognized  as  stated  on 
page  80  under  oxalates. 

It  is  evident  from  what  has  just  been  said,  that  a  knowl- 
edge of  the  solubility  of  chemical  compounds  is  of  great 
value  in  determining  the  presence  or  absence  of  various 
classes  of  salts.  The  student  of  qualitative  analysis  should 
always  have  at  hand  a  copy  of  some  work  on  general  chem- 
istry to  which  he  can  turn ;  but  for  convenience  of  reference, 
a  table  will  be  found  on  pages  108,  109,  in  which  are  stated 
in  a  general  way  the  solubilities  of  the  more  commonly 
occurring  salts. 

It  is  to  be  distinctly  borne  in  mind  that  this  table  is  not 
exhaustive,  and  is  intended  merely  as  a  help  to  the  beginner, 


108       SOLUBILITIES  OF  CHEMICAL  COMPOUNDS.      §87 


TABLE  OP 


Ala  [NB> 

]  Sb 

As 

Ba 

Bi 

Cd  Ca 

Cra 

Co 

Cu 

Au 

Fe» 

[*..]- 

Acetate 

Wi 

W 

U 

U 

w 

w 

w    w 

Wl 

W 

Wl 

U 

W 

Wl 

Arseni&te 

A 

W 

tr 

U 

(W) 

(A) 

U       A 

A 

A 

A 

U 

A 

A 

Arsenite 

U 

w 

u 

u 

(W) 

U 

F     (W) 

U 

A 

A 

u 

A 

A 

A 

Borate 

U 

w 

u 

u 

(W) 

A 

(W)   (W) 

A 

(W) 

(W) 

u 

A 

A 

A 

A 

A 

Bromide 

W 

w 

(W) 

(W) 

w 

(W) 

W      W 

W 

W 

W4 

w 

W 

W 

A 

A 

A 

Carbonate 

U 

w 

U 

U 

A 

A 

A       A 

A 

A 

A 

u 

A 

A 

Chlorate 

W 

w 

U 

u 

W 

U 

,w    w 

U 

W 

W 

u 

W 

W 

Chloride 

W 

w 

w 

A 

W 

Wl 

w    w 

W 

W 

W 

w 

W 

W 

Al 

Chromate 

A 

w 

A 

U 

A 

A 

(W)    W 

A 

A 

(W) 

u 

u 

A 

Cyanide 

U 

w 

U 

u 

(W) 

U 

(W)     W 

A 

A 

A 

W6 

(A) 

W 

Fluoride 

I 

w 

W 

w 

(W) 

W 

(W)      I 

W-, 

(W) 

(W) 

u 

(W) 

(W) 

W1 

AT 

A/"tTT\ 

A 

A 

A 

HydrutG 
Hyposulph- 

, 

U 

w 

—  JL 

u 

u 

(W) 
(W) 

U 

(.  "  ) 

w    w 

U 

W 

U 

u 

W 

, 
F 

ite 

A 

Iodide 

w 

w 

A 

(W) 

W 

A 

w    w 

W 

W 

TJ4 

A 

W 

W 

Nitrate 

w 

w 

U 

u 

w 

Wl 

w    w 

W 

W 

W 

w 

W 

W 

Oxalate 

A 

w 

U 

u 

A 

A 

A       A 

W 

A 

A 

u 

A 

A 

Oxide 

A 

w 

A 

w 

W 

A 

A     (W) 

A-I 

A 

A 

A 

A 

A 

Phosphate 

A 

w 

(W) 

u 

A 

A 

A       A 

A 

A 

A 

U 

A 

A 

A 

Silicate 

A-I 

U 

U 

u 

A-I 

IT 

TT     A-I 

U 

U 

A-I 

u 

(A)-I 

(A)-I 

Sulphate 

W 

w 

A 

u 

I 

A 

W    (W) 

W 

W 

W 

u 

W 

Wl 

Sulphide 

U 

w 

A 

A 

W 

A 

A      W 

U 

A 

A 

A 

A 

U 

Sulphite 

W 

w 

U 

u 

A 

A 

A     (W) 

A 

A 

A 

u 

(W) 

A 

Tartrate 

W 

w 

W 

u 

(W) 

A 

A 

(W)   (W) 

W 

W 

(W) 

u 

(W) 

W 

Ala  | 

:NH* 

]  Sb 

As 

Ba 

Bi 

Cd  Ca 

Cra 

Co 

Cu 

Au 

*" 

[Fe-2  ]*» 

In  this  table  W  signifies  that  the  substance  is  readily 
soluble  in  water,  (W)  that  the  substance  is  soluble  with 
difficulty  in  water ;  A  and  (A)  that  the  substance  is 
readily  or  with  difficulty  dissolved  by  acids  ;  I  that  the  sub- 
stance is  insoluble  in  water  or  acids ;  U  signifies  that  the 
compound  is  either  unknown  or  so  uncommon  as  rarely  to  be 
met  with. 


§87     SOLUBILITIES  OF  CHEMICAL  COMPOUNDS.       1Q9 


SOLUBILITIES. 


Pb  Mg 

Mn  [Hga  ]« 

Hg«  Mi 

Pb 

K 

Ag 

Ma  Sr 

Sn" 

Sn*  Zn 

W      W 

"W        (W) 

W      W 

U 

w 

(W) 

W 

w 

W 

W 

w 

Acetate 

A       A 

A          A 

A       A 

U 

w 

A 

W 

(W) 
A 

A 

A 

A 

Areeniate 

A       A 

A          A 

A       A 

U 

w 

A 

W 

A 

A 

A 

U 

Ar'senite 

A       A 

(W)        U 

U       A 

U 

w 

(W) 

W2 

(W) 

A 

U 

A 

Bbrate 

A 

(W)     W 

W         A 

(W)     W 

w 

w 

(A) 

w 

W 

W 

W 

W 

Bromide 

A       A 

A          A 

A       A 

A 

W2 

A 

W2 

A 

A 

A 

A 

Carbonate 

W      "W 

U         W 

W      W 

U 

w 

W 

w 

W 

W 

W 

W 

Chldrate 

(W)     W 

W        (A) 

W      W 

3V 

w 

(A)-I 

w 

W 

W 

w 

W 

Chloride 

A      W 

U          A 

(W)     W 

U 

W2 

A 

w 

(W) 

A 

A 

w 

Chromate 

A 

A       W 

A          U 

W     (A) 

(A) 

w 

A 

w 

U 

U 

U 

A 

Cyanide 

A      (A) 

A          A 

"W     (W) 
A 

W 

w 

W 

w 

(W) 

W 

w 

(W) 

.A. 

Fluoride 

(W)     A 

A          A 

A       A 

A 

Iw 

A 

w 

(W) 

A 

A 

A 

Hydrate 

A 

(W)     W 

A 

W         U 

U       W 

U 

w 

(W) 

w 

w 

W 

U 

TJ 

Hyposulphite 

(W)     W 

W         A 

A       W 

I 

w 

A 

w 

w 

(W) 

(W) 

W 

Iodide 

w    w 

W        W 

W      W 

W 

w 

W 

w 

w  . 

A 

A 

W 

Nitrate 

A     (W) 

(W)        A 

A       A 

W 

W2 

(W) 

w 

A 

A 

W 

A 

Oxalate 

A 

A 

A 

A       A 

A          A 

A       A 

A 

w 

A 

w 

(W) 

A 

I 

A 

Oxide 

A       A 

A          A 

A       A 

U 

w 

A 

w 

A 

A 

A 

A 

Phosphate 

U        I 

(A)  -I       U 

U       U 

U 

w 

U 

w 

A 

U 

U 

A-I 

Silicate 

I       W 

W         W 

W      W 

w 

W2 

(W) 

w 

I 

W 

"W 

W 

Sulphate 

A      W 

A          A 

A       A 

A 

w 

A 

w 

W 

A 

A 

A 

Sulphide 

A     (W) 

(W)        W 

W      A 

U 

w 

A 

w 

A 

W 

U 

A 

Sulphite 

A       W 

(W)         A 

(W)     A 

U 

W3 

A 

w 

W 

(W) 

A 

(W) 
A. 

Tartrate 

Pb  Mg 

Mn  [Hg2  ]» 

Hg«  Mi 

Pt 

K 

Ag 

Ma   Sr 

Sn» 

Sn 

'  Zn 

1 

The  basic  salt  is  A. 

4 

The 

-ous  salt  is 

A. 

2 

The  acid  salt  is 

W. 

5 

The 

-ous  salt  is 

I. 

3    The  acid  salt  is 

(W). 

10 

110  INSOLUBLE  SUBSTANCES.  §§  88,  89 

who  is  analyzing  comparatively  simple  substances.  In  the 
case  of  complex  mixtures  the  table  is  of  little  service.  Thus, 
chloride  of  silver  is  designated  as  I,  but  it  would  be  easy  to 
mix  chloride  of  silver  and  chloride  of  sodium  in  such  propor- 
tions that  on  treatment  with  water  the  whole  of  the  mixture 
would  go  into  solution  :  so  too  the  chlorides  of  potassium 
and  platinum  are  readily  soluble  in  water,  each  by  itself,  but 
the  double  chloride  of  these  two  elements  is  so  insoluble  that 
it  is  used  as  a  test  for  potassium  (§  42)  and  for  platinum 
(§  96). 


.      TREATMENT   OF   INSOLUBLE    SUBSTANCES. 

88.  The   substances  of  common   occurrence  which  are 
practically  insoluble  in  water  and  acids  are  :  — 

The  sulphates  of  barium,  strontium  and  lead. 

Chloride  of  silver. 

The  anhydrous  sesquioxides  of  aluminum,  chromium  and 
iron,  either  native,  or  the  result  of  intense  ignition. 

Chrome-iron-ore,  a  native  mineral. 

Some  aluminates. 

Binoxide  of  tin,  native,  or  the  result  of  ignition. 

Silica  and  many  silicates. 

Fluoride  of  calcium  (fluor-spar)  . 

Besides  the  substances  included  in  this  list,  sulphur  and 
carbon,  or  graphite,  should,  perhaps,  be  mentioned,  because 
they  are  insoluble  ;  but  they  will  have  been  detected  during 
the  preliminary  blowpipe  examination,  and  their  presence 
allowed  for.  Bromide,  iodide  and  cyanide  of  silver  are  de- 
composed by  boiling  with  aqua  regia,  and  converted  into  the 
chloride,  so  that  these  substances  never  appear  in  their  proper 
form  in  the  final  insoluble  residue. 

89.  Substances  which  resist  solution  in  liquids  are  gen- 
eralty  liquefied  by  the  action  of  fluxes  at  a  high  temperature  ; 
they  are  fused  in  contact  with  some  powerful  decomposing 
agent,  like  the  carbonate  or  acid  sulphate  of  an  alkali-metal, 


§  89  INSOLUBLE  SUBSTANCES.  HI 

or  the  h}Tdrate  or  carbonate  of  an  alkaline-earth  metal.  Cer- 
tain preliminary  experiments  should  precede  the  fusion. 

The  insoluble  powder  is  first  examined  carefully  (with  the 
help  of  a  lens,  if  convenient)  to  ascertain  if  it  is  a  homo- 
geneous substance  of  the  same  color  throughout,  or  a  mixture 
composed  of  dissimilar,  variously-colored  particles.  The  fol- 
lowing blowpipe  experiments  sometimes  give  decisive  indica- 
tions, particularly  with  homogeneous  substances. 

a.  The  reduction  test  (§  81)  is  repeated  with  great  care, 
looking  especially  for  silver,  lead  and  tin,  and  applying  to 
the  globule,  if  any  is  obtained,  the  test  for  distinguishing 
between  these  three  white  metals.  This  test  has  already 
been  applied  to  the  original  substance  ;  but  if  this  substance 
was  a  complex  mixture  containing  soluble  ingredients,  it  is 
quite  possible  that  the  test  should  give  a  more  satisfactory 
result,  now  that  all  substances  soluble  in  water  and  acids  have 
been  removed,  than  it  yielded  before.  If,  however,  decided 
indications  of  the  presence  of  a  reducible  metal  were  obtained 
in  the  first  instance,  the  repetition  of  the  test  is,  of  course, 
unnecessary.  If  any  reducible  metal  is  detected,  it  is  neces- 
sary to  use  a  porcelain  crucible  for  the  fusion  which  it  may 
be  desirable  to  make  (§  90)  in  order  to  convert  the  insoluble 
substance  into  a  more  manageable  form.  A  platinum  cruci- 
ble, which  is  emplo3^ed  for  most  fusions,  cannot  be  used  with 
safety  when  the  substance  to  be  fused  contains  any  reducible 
metal ;  for  many  of  the  alloys  of  platinum  are  extremely 
fusible. 

Sometimes,  when  the  substance  under  examination  contains 
but  a  small  proportion  of  metal,  some  metal  may  be  reduced 
during  the  blowpipe  experiment  on  charcoal,  but  the  detached 
particles  may  not  run  together  into  a  single  conspicuous 
globule.  Since  a  mistake  as  to  the  presence  of  a  reducible 
metal  may  involve  the  destruction  of  a  platinum  crucible,  it 
is  best  in  doubtful  cases  to  operate  in  a  more  delicate  fashion. 
To  ascertain,  beyond  question,  whether  any  reduced  metal  has 
been  separated  in  this  experiment,  moisten  the  cavity  in  the 


112  INSOLUBLE  SUBSTANCES.  §  89 

charcoal  with  water  after  the  fusion  has  been  finished,  cut  the 
charcoal  out  for  a  little  distance,  both  around  and  below  the 
cavity,  and  transfer  the  contents  of  the  cavity  and  the  scraps 
of  charcoal  to  an  agate  or  porcelain  mortar.  Pulverize  the 
whole  mass,  and  then  carefully  wash  away  the  powdered 
charcoal  and  all  the  lighter  portion  of  the  mixture.  Any 
malleable  metal  that  may  have  been  reduced  remains  in  the 
mortar  in  little  flattened  grains  or  spangles,  in  which  the 
peculiar  color  and  lustre  of  the  metal  or  alloy  are  generally 
visible.  Sometimes  metallic  streaks  are  produced  on  the 
mortar  or  pestle  by  little  particles  of  metal  ground  between 
them.  The  student  must  not  mistake  glistening  particles  of 
wet  charcoal  sticking  to  the  mortar  or  pestle  for  metallic 
spangles,  and  the  metal  should  be  thoroughly  removed  from 
both  mortar  and  pestle  by  the  use  of  a  few  drops  of  warm 
aqua  regia,  immediately  after  the  experiment  is  finished,  in 
order  to  avoid  errors  on  a  subsequent  occasion. 

b.  Prepare  another  pellet  of  a  mixture  of  equal  parts  of 
the  insoluble  powder  and  carbonate  of  sodium,  adding  a  little 
charcoal  powder  to  the  paste.  Fuse  this  mixture  upon  char- 
coal in  the  reducing  flame  of  the  blowpipe.  Scoop  out  the 
fused  mass  and  the  surrounding  charcoal  with  a  penknife, 
place  the  dry  mass  upon  a  bright  surface  of  silver  (coin  or 
foil) ,  and  wet  it  with  a  drop  of  water.  If  a  brown  stain  be 
produced  on  the  silver,  it  is  evidence  of  the  presence  of  sul- 
phide of  sodium  in  the  fused  mass.  This  sulphide  results 
from  the  reduction  of  a  sulphate,  and  is  evidence  of  the 
presence  of  a  sulphate  in  the  substance  tested.  The  odor  of 
sulphuretted  hydrogen  is  often  perceptible  when  the  fused 
mass  is  moistened.  The  silver  coin  or  foil  may  be  replaced 
by  a  piece  of  lead  paper,  if  care  be  taken  not  to  mistake  the 
mere  dirtying  of  the  paper  for  a  stain  of  sulphide  ;  the  silver 
is,  however,  to  be  preferred ;  it  may  be  cleaned  after  use  by 
treating  it  with  a  solution  of  cyanide  of  potassium  and  then 
washing  with  water.  It  is  obvious  that  the  carbonate  of 
sodium  used  in  this  test  must  be  so  free  from  sulphate  of 


§  89  INSOLUBLE  SUBSTANCES.  113 

sodium  as  not  itself  to  give  this  reaction  on  silver,  after  fusion 
on  charcoal.  Since  coal-gas  invariably  contains  traces  of 
sulphur  compounds,  the  test  cannot  be  performed  with  a  gas- 
flame  ;  a  candle  or  lamp  flame  (App.,  §  78)  must  be  em- 
ployed. 

It  is,  of  course,  possible  to  apply  this  test  for  sulphates  to 
the  fused  mass  obtained  in  (a)  ;  this  second  test  is  in  fact 
unnecessary  when  a  decided  reaction  has  been  obtained  in 
in  the  first  instance. 

c.  Make  the  loop  on  the  end  of  the  bit  of  platinum  wire 
(App.^§  79)  white-hot  in  the  blowpipe  flame,  and  thrust  it 
white-hot  into  some  powdered  borax  ;  a  quantity  of  borax  will 
adhere  to  the  hot  wire ;  reheat  the  loop  in  the  oxidizing 
flame  ;  the  borax  will  puff  up  at  first,  and  then  fuse  to  a  trans- 
parent glass.  If  enough  borax  to  form  a  solid,  transparent 
bead  within  the  loop  does  not  adhere  to  the  hot  wire  the  first 
time,  the  hot  loop  may  be  dipped  a  second  time  into  the  pow- 
dered borax. 

When  a  transparent  glass  has  been  formed  within  the  loop 
of  the  platinum  wire,  touch  the  bead  of  glass  while  it  is  hot 
and  soft,  to  a  few  particles  of  the  insoluble  powder,  and  re- 
heat the  bead  with  the  adhering  powder  in  the  oxidizing 
flame.  If  the  substance  dissolves  slowly  in  the  borax,  and 
the  bead  has  a  fine  yellowish-green  color  when  cold,  chromium 
is  probably  present.  Reheat  the  bead  in  the  reducing  flame  : 
if  it  presents  a  bright  green  color  both  when  hot  and  cold, 
there  is  no  doubt  of  the  presence  of  chromium. 

It  sometimes  happens  when  too  much  of  the  substance  to 
be  tested  has  been  added,  that  the  borax  bead  becomes  so 
dark-colored  as  to  be  practically  opaque.  It  may  then  be 
flattened  while  soft,  by  sudden  pressure  between  any  smooth 
metallic  surfaces,  like  the  flat  parts  of  jewellers'  tweezers. 
If  the  flattening  makes  the  color  of  the  borax-glass  visible, 
nothing  more  is  necessary ;  but  if  the  glass  is  still  too  dark, 
all  the  glass  outside  the  loop  of  platinum  may  be  broken  off 
by  gentle  hammering,  and  the  remaining  glass  may  be  re- 
heated and  largely  diluted  by  the  addition  of  more  borax. 


114        INSOLUBLE  SUBSTANCES. —  FUSIONS.  §§89,90 

It  is  convenient  to  be  informed  of  the  presence  of  chromium, 
because  chromic  oxide  and  chrome-iron-ore  are  substances 
which  it  is  particularly  difficult  to  decompose  effectually  by 
fusion.  In  presence  of  chromium,  no  other  bead-reaction 
which  can  be  anticipated  under  the  circumstances  will  give  a 
decisive  result ;  but  in  the  absence  of  chromium,  the  presence 
of  iron  may  be  determined,  A  suitable  quantity  of  oxide  of 
iron  causes  the  borax-bead,  heated  in  the  oxidizing  flame,  to 
look  red  when  hot  and  yellow  when  cold.  In  the  reducing 
flame  the  iron  bead  becomes  greenish,  or  light  brownish- 
green. 

This  test  is  rendered  unnecessary  if  the  substance  under 
examination  be  a  white  powder,  or  if  from  other  appearances 
the  absence  of  chromium  is  assured. 

d.  The  test  for  fluorine  (§70)  should  be  applied  to  the 
original  substance,  if  it  has  not  already  been  done. 

When  all  the  above-mentioned  tests  (a-d)  give  negative 
results,  the  simplification  of  the  problem  is  very  conspicuous  ; 
the  substances  which  may  be  present  are  reduced  to  alumina 
and  some  aluminates,  silica  and  silicates.  Again,  in  the  case 
of  a  substance  evidently  homogeneous,  if  the  preliminary 
tests  give  affirmative  results,  the  indications  of  the  character 
of  the  substance  are  almost  conclusive.  Thus  chloride  of 
silver,  sulphate  of  lead,  chromic  or  ferric  oxide,  binoxide  of 
tin,  or  fluoride  of  calcium,  may  be  satisfactorily  identified  by 
the  preliminary  tests  alone. 

There  are  two  methods  of  changing  insoluble  substances 
into  more  manageable  forms  by  the  application  of  heat  with 
sufficient  exactness  for  the  purposes  of  the  qualitative  analyst, 
—  the  method  by  fusion,  and  the  method  by  deflagration. 

90.  Fusions. — Mix  the  fine  powder  of  the  insoluble  sub- 
stance with  about  six  parts  by  weight  of  dry  carbonate  of 
sodium  in  powder.  Both  powders  must  be  as  fine  as  they  can 
be  made,  and  they  must  be  intimately  mixed.  Keep  the  mix- 
ture at  a  bright  red  heat,  in  a  platinum  crucible  (a  porcelain 


§  91          FUSION  OF  INSOLUBLE  SUBSTANCES.  H5 

crucible,  if  a  reducible  metal  has  been  found  in  the  substance, 
§  89,  a.),  and  fusion  is  for  any  reason  preferred  to  deflagra- 
tion, until  the  mass  has  been  brought  to  a  state  of  quiet 
fusion  (App.,  §  75).  Place  the  hot  platinum  crucible,  when 
withdrawn  from  the  lamp  or  fire,  on  a  cold  block,  or  thick 
plate  of  iron,  and  let  it  cool.  If  a  gas  blast-lamp  be  em- 
ployed, the  supply  of  gas  may  be  interrupted,  and  the  blast 
of  air,  directed  as  before,  upon  the  crucible,  until  it  has 
become  cold. 

When  the  green  borax  bead,  and  the  dark  color  of  the 
insoluble  powder,  point  to  the  presence  of  chrome-iron-ore,  a 
mixture  of  two  parts,  by  weight,  of  carbonate  of  sodium 
with  two  parts,  by  weight,  of  nitre,  may  be  substituted  for 
the  four  parts  of  carbonate  of  sodium  alone. 

91.  Treatment  of  the  Fused  Mass.  —  When  the  cru- 
cible has  been  cooled  in  the  way  mentioned  above,  the  fused 
mass  can  generally  be  removed  from  the  crucible  in  an 
unbroken  lump.  Soak  the  lump  in  boiling  water  until  every- 
thing is  dissolved  which  is  soluble  in  water.  If  the  mass 
cannot  be  detached  from  the  crucible,  the  crucible  and  its 
contents  must  be  soaked  in  boiling  water. 

The  aqueous  solution  of  the  fused  mass  is  filtered  from  the 
residue  insoluble  in  water  and  reserved.  That  portion  of  the 
fused  mass  which  boiling  water  did  not  dissolve  is  treated 
with  acid,  —  chlorhydric  acid  if  silver  and  lead  be  absent, 
nitric  acid  if  either  of  these  metals  be  present,  —  and  the 
acid  solution  obtained  is  treated  as  will  be  described.  If  a 
portion  of  the  fused  mass  resist  both  water  and  acids,  the 
insoluble  portion  may  consist  of  separated  silicic  acid,  or  of 
some  of  the  original  substance  undecomposed  by  the  fusion. 
In  the  latter  case,  another  and  more  prolonged  fusion  is  the 
only  effectual  remedy,  although  it  may  often  happen  that  a 
partial  decomposition  of  the  insoluble  substance  will  enable 
the  analyst  to  recognize  all  the  elements  which  it  contains. 

The  treatment  of  the  aqueous  and  acid  solutions  of  the  last 
paragraph  will  be  best  understood  if  we  first  consider  what 


116          FUSION  OF  INSOLUBLE  SUBSTANCES.          §  91 

changes  take  place  in  the  process  of  fusion.  Suppose  that 
the  substance  in  hand  is  sulphate  of  barium ;  at  the  high 
temperature  of  the  fusion  the  barium  and  sodium  change 
places  and,  instead  of  sulphate  of  barium  and  carbonate  of 
sodium,  there  result  carbonate  of  barium  and  sulphate  of 
sodium  :  BaSO4  +  NaCO3  =  NaSO4  -f  BaCO3.  When  the 
fused  mass  is  treated  with  water,  the  sulphate  of  sodium 
(with  the  excess  of  carbonate  of  sodium)  goes  into  solution, 
while  the  carbonate  of  barium,  which  is  insoluble  in  water,  is 
dissolved  by  the  chlorhydric  (or  nitric)  acid  as  chloride  (or 
nitrate)  of  barium.  Therefore  in  a  case  like  this,  the  metallic 
element  would  be  found  in  the  acid  solution  and  the  class  or 
kind  of  salt  might  be  determined  by  apptying  the  test  for 
sulphates  to  the  aqueous  solution.  Again,  suppose  the  sub- 
stance under  examination  is  a  double  silicate  of  calcium  and 
aluminum.  After  fusion  with  carbonate  of  sodium  and  treat- 
ment successively  with  water  and  acid,  a  portion  of  the  silicic 
acid  will  be  in  the  aqueous  solution  (as  silicate  of  sodium) 
and  a  portion  in  the  acid  solution,  while  a  part  may  remain 
insoluble ;  the  aluminum  will  exist  partly  in  the  aqueous 
solution  (a&  aluminate  of  sodium)  and  partly  in  the  acid  so- 
lution (as  chloride  of  aluminum)  ;  the  calcium,  which  after 
the  fusion  remained  as  carbonate,  insoluble  in  water,  will  havo 
been  converted  into  chloride  and  will  be  found  in  the  acid 
solution.  Having  considered  the  general  nature  of  the 
changes  brought  about  by  fusion  with  carbonate  of  sodium, 
we  proceed  to  the  statement  of  the  treatment  of  the  aqueous 
and  acid  solutions  of  the  fused  mass. 

a.  If  the  test  for  sulphates  described  in  §  89,  b,  on  page 
112,  has  failed  to  give  satisfactory  indications,  acidify  a  small 
portion  of  the  aqueous  solution  with  chlorhydric  acid,  and 
apply  the  barium  test.     The  carbonate  of  sodium  used  in  the 
fusion  should  be  free  from  sulphate. 

b.  Acidify  another  small  portion  with  acetic  acid,  and 
apply  the  lead  test  for  chromates  (§  62).     In  presence  of 
sulphuric  acid  this  test  will  be  obscured,  but  not  rendered 
wholly  useless  (§  30,  p.  40). 


§  91         FUSION  OF  INSOLUBLE  SUBSTANCES.  H7 

c,  Acidify  a  third  portion  with  nitric  acid,  and  apply  the 
silver  test  for  chlorine.     The  student  must  first  prove  that  his 
carbonate  of  sodium  contains  no  chloride. 

d.  If  the  test  for  fluorine  by  the  method  of  §  68  has,  for 
any  reason,  been  unsatisfactory,  a  fourth  portion,  having  been 
concentrated  by  evaporation  in  a  porcelain  dish,  and  again 
cooled,  is  acidified  with  chlorhydric  acid,  and  then  left  at  rest 
until  the  carbonic  acid  has  escaped.     It  is  then  supersatu- 
rated with  ammonia,  heated,  and  filtered  while  hot.     The 
filtrate  is  collected  in  a  bottle  ;  chloride  of  calcium  is  imme- 
diately added  to  it ;  the  bottle  is  closed  and  allowed  to  stand 
at  rest.     If  the  original  substance  contained  a  fluoride,  the 
fluorine  will  have  combined  with  sodium  during  the  fusion* 
and  fluoride  of  sodium  will  be  contained  in  the  aqueous  solu- 
tion.    The  carbonic  acid  having  been  expelled,  and  all  sub- 
stances precipitable  by  ammonia  having  been  removed,  the 
chloride  of  calcium  will  throw  down  the  fluoride  of  calcium. 
If  a  precipitate  separates  from  the  liquid  in  the  bottle  after 
some  time,  it  is  collected  in  a  small  filter,  dried  and  examined 
for  fluorine  by  the  method  of  §  68. 

When  the  tests  a-d  give  negative  results,  or  when  by  pre- 
vious tests  the  absence  of  sulphates,  chromates,  chlorides 
and  fluorides  is  made  certain,  the  remainder  of  the  aqueous 
solution  is  added  to  the  acid  solution  and  the  mixture  is 
evaporated  to  dryness  and  ignited  ;  the  residue  thus  obtained 
is  boiled  with  dilute  chlorhydric  (or  nitric)  acid.  If  the 
dilute  acid  fails  to  dissolve  the  residue  completely,  the  insolu- 
ble portion  consists  of  silicic  acid.  The  solution  is  examined 
in  the  usual  way  for  the  metallic  elements  (§  44),  except,  of 
course,  sodium  (and  sometimes  potassium),  which  has  been 
added  in  the  flux.  (See  §  92,  p.  118). 

When  the  preliminary  examination  or  the  tests  a-d  show 
the  presence  of  one  or  more  of  the  classes  of  salts  mentioned 
above,  the  treatment  is  slightly  different.  In  that  case  the 
remainder  of  the  aqueous  solution  is  acidified  with  chlor- 
hydric acid,  evaporated  to  dryness  and  ignited;  the  residue 


118        FUSION  OF  INSOLUBLE  SUBSTANCES.    §§  91,92 

thus  obtained  is  boiled  with  dilute  chlorhydric  acid.  If  the 
dilute  acid- fails  to  dissolve  the  residue  completely,  the  insolu 
ble  portion  consists  of  silicic  acid.  The  solution  is  tested 
for  the  metallic  elements  in  the  usual  manner.  If  silicic  acid 
has  been  found  in  the  aqueous  solution,  the  acid  solution  is 
evaporated  to  dryness  and  ignited :  the  residue  is  treated 
with  dilute  acid  and  the  solution  after  being  filtered  from  the 
silicic  acid  is  examined  for  the  metallic  elements  in  the  usual 
manner.  It  is  evidently  impracticable  in  this  last  case  to 
mix  the  aqueous  and  the  acid  solutions,  for  if  the  case  of 
sulphate  of  barium  (p.  116)  be  taken  as  an  example,  in  mix- 
ing the  aqueous  solution  (containing  sulphate  of  sodium)  and 
the  acid  solution  (containing  chloride  of  barium),  there 
would  be  an  immediate  precipitation  of  the  insoluble  sulphate 
of  barium  which  was  the  substance  to  be  analyzed. 

Silicates  are  by  far  the  most  common  of  insoluble  sub- 
stances. A  great  variety  of  metallic  elements  occur  in 
insoluble  silicious  minerals,  so  that  the  possible  contents  of 
the  acid  solution  of  the  fused  mass  are  very  various.  The 
evaporation  to  dryness  in  order  to  render  the  silica  insoluble 
is  prescribed  because  the  subsequent  examination  goes  on 
the  better  for  this  preliminary  removal  of  silica,  which,  if  left 
in  solution,  might  create  confusion  by  appearing  as  a  precipi- 
tate at  almost  any  stage  of  the  analysis. 

Many  silicates  contain  sodium  and  potassium.  When  the 
presence  or  absence  of  these  alkali-metals  is  to  be  determined, 
it  is  evident  that  the  pulverized  silicate  must  not  be  fused 
with  carbonate  of  sodium,  but  with  some  decomposing  flux 
free  from  alkali. 

92.  Decomposition  by  Means  of  Carbonate  of  Cal- 
cium and  Chloride  of  Ammonium.  —  An  intimate  mixture 
is  prepared  of  one  part  of  the  silicate,  six  parts  of  pure  pre- 
cipitated carbonate  of  calcium,  three  fourths  part  of  pul- 
verized chloride  of  ammonium.  This  mixture  is  heated  to 
bright  redness  in  a  platinum  crucible  for  thirty  or  forty  min- 
utes. The  crucible  with  its  contents  (which  should  be  in  a 


§§93,94  INSOLUBLE  SUBSTANCES.  H9 

coherent,  sintered,  but  not  thoroughly  fused  condition),  is 
then  placed  in  a  beaker,  and  soaked  for  half  an  hour  in  water 
*kept  near  the  boiling  point.  The  contents  of  the  beaker  are 
then  filtered.  The  filtrate,  containing  caustic  lime,  chloride 
of  calcium,  and  all  the  sodium  and  potassium  of  the  original 
silicate  as  chlorides,  is  treated  with  a  little  ammonia-water, 
and  with  carbonate  of  ammonium  in  slight  excess  ;  the  liquid 
is  heated  to  boiling  and  filtered.  This  second  filtrate  is 
evaporated  to  dryness,  and  gently  ignited  to  expel  the  am- 
monium salts.  The  residue  is  dissolved  in  a  little  water ; 
one  or  two  drops  of  carbonate  of  ammonium,  and  a  drop  of 
oxalate  of  ammonium  are  then  added ;  the  mixture  is  again 
heated  and  filtered ;  this  third  filtrate  is  evaporated  to  dry- 
ness  and  ignited ;  the  ignited  residue,  if  there  be  any, 
consists  of  the  chlorides  of  sodium  and  potassium,  or  of  one 
of  these  two  salts.  This  residue  is  examined  according 
to  §  42. 

93.  Fusion  with.  Acid  Sulphate  of  Sodium,  —  The 
following  method  may  be  tried   to  advantage   upon  ferric 
oxide,   chromic   oxide,  or  chrome-iron-ore,  and   some  very 
refractory  silicates.     Heat  the  insoluble  substance  with  three 
or  four  times  its  bulk  of  acid  sulphate  of  sodium  ( App.,  §  29) 
in  a  platinum  crucible,  until  the  sulphate  melts ;  then  main- 
tain it  in  the  liquid  state  for  half  an  hour.     This  operation 
should  be  performed   under   a  hood.     The  fused  mass   is 
treated  essentially  as  before  (§91),  allowance  being  made  for 
the  different  nature  of  the  flux. 

94.  Deflagration.  —  The  method  of  fusion  just  described 
involves  the  use  of  a  platinum  or  porcelain  crucible,  and  de- 
mands the  heat  of  a  blast-lamp,  or  strong  coal  fire.     Neither 
crucibles,  lamps  nor  fires  are  necessary  in  the  method  of 
deflagration,  which  applies  the  _heat  inside  the  mass  to  be 
fused.     This  decomposition  by  deflagration  is  performed  as 
follows :     One  part,  by  weight,  of  the  insoluble  powder  is 
intimately  mixed  with  two  parts  of  dry  carbonate  of  sodium, 
two  parts  of  fine  and  pure  charcoal  powder,  and  twelve  parts 


120  DEFLAGRATION:  §  94 

of  powdered  nitre.  The  mixture  is  put  in  a  thin  porcelain 
dish  or  clean  iron  tray;  the  dish,  or  little  tray,  is  placed 
under  a  hood,  or  in  the  open  air,  and  a  lighted  match  is 
applied  to  the  centre  of  the  heap.  The  deflagration  is  com- 
pleted in  two  or  three  seconds,  and  a  well-fused  mass 
remains.  This  mass  is  detached  from  the  cooled  dish  or 
tray,  and  boiled  with  water  in  a  beaker ;  it  is  generally  very 
porous,  and  is  therefore  readily  disintegrated  by  stirring  it  in 
the  hot  water  with  a  glass  rod.  The  soluble  portion  will  all 
be  extracted  in  a  very  few  minutes.  The  residue  left  by 
water  is  treated  with  acid  precisely  as  described  in  §  91. 
The  aqueous  and  acid  solutions  of  the  deflagrated  substance 
are  submitted  to  the  same  operations  as  the  corresponding 
solutions  of  substances  fused  in  crucibles.  A  little  charcoal 
is  generally  left  undissolved  by  the  acid,  and  with  it  any  of 
the  substance  which  may  have  escaped  decomposition.  The 
mixture  of  one  part,  by  weight,  of  powdered  charcoal,  and 
six  parts  of  nitre,  may  be  kept  ready  mixed  for  effecting  the 
fusion  of  insoluble  substances. 

The  advantages  of  this  process  are  that  it  is  quick, 
requires  only  cheap  and  common  tools,  and  may  be  applied 
to  substances  containing  reducible  metals,  as  well  as  to 
any  others.  It  is,  of  course,  inapplicable  when  sodium  and 
potassium  are  to  be  sought  for  in  silicates.  Chrome-iron-ore 
cannot  be  decomposed  in  this  way.  The  insoluble  sulphates, 
chloride  of  silver,  binoxide  of  tin,  fluorspar,  glass,  and  many 
natural  silicates,  may  be  very  well  treated  by  this  method,  in 
spite  of  its  apparent  roughness. 


§§95,96  METALS  AND  ALLOTS.  121 


CHAPTER  XII. 

TREATMENT  OP  A  PURE  METAL  OR  ALLOY. 

95.  THE  elements  which  are  now  used  in  the  arts  in  the 
metallic  state,  and  which  therefore  may  come  into  the  hands 
of  the  analyst  as  metals,  either  pure  or  alloyed,  are  silver, 
lead,  mercury,  bismuth,  cadmium,  copper,  arsenic,  antimony, 
tin,  gold,  platinum,  aluminum,  iron,  zinc,  nickel  and  mag- 
nesium. These  metals  can  all  be  brought  into  solution  and 
detected  in  the  wet  way  with  ease  and  certainty.  It  is  there- 
fore not  worth  while  to  submit  a  metal,  or  metallic  alloy,  to 
preliminary  blowpipe  tests,  although  at  need  mercury  and 
arsenic  can  be  readily  detected  by  the  closed-tube  test  (§  80), 
and  many  others,  by  exposing  them  on  charcoal  to  the  re- 
ducing and  oxidizing  flame  (compare  §  81,  pp.  95-97). 

A  portion  of  the  metal  or  alloy  to  be  examined  should  first 
be  reduced  to  as  fine  a  state  of  division  as  possible.  If  it  is 
brittle,  it  can  be  powdered ;  if  soft,  shavings  can  be  cut  from 
it ;  if  tough  and  hard,  it  can  perhaps  be  fused,  and  shaken 
into  powder  while  melted,  or  granulated  by  being  poured  from 
a  height  into  cold  water.  Filings  should  be  the  last  resort, 
because  of  the  possibility  of  foreign  admixture  of  iron. 

98.  Action  of  Nitric  Acid  on  the  Metals, — A  small 
quantity  of  the  divided  metal  or  alloy,  about  the  equivalent 
of  a  pea  in  bulk,  is  placed  in  a  flask,  covered  with  concen- 
trated nitric  acid,  and  heated  gently  under  a  hood  or  in  the 
open  air  for  half  an  hour. 

//  complete  solution  ensues,  gold,  platinum,  tin  and  anti- 
mony are  probably  altogether  absent ;  they  can  only  be  pres- 
ent in  very  minute  proportion.  Any  of  the  other  metals 
above  enumerated  may  be  present.  Transfer  the  acid  solu- 
11 


122  TREATMENT  OF  ALLOTS.  §  96 

tion  to  a  porcelain  dish,  and  evaporate  it  almost  to  dryness  ; 
dilute  the  evaporated  liquid  with  about  ten  times  its  bulk  of 
water,  and  proceed  with  the  analysis  in  the  usual  way  (§  44). 
If  the  solution,  from  which  the  greater  part  of  the  free  acid 
has  been  removed  by  evaporation,  becomes  turbid  on  the 
addition  of  water,  bismuth  is  doubtless  present.  In  this  case 
enough  acid  must  be  restored  to  the  solution  to  clarify  it. 
Mercury,  if  present,  will  be  dissolved  to  mercuric  nitrate. 

If  a  residue  remains  undissolved,  add  a  little  more  acid  to 
make  sure  that  the  acid  is  incapable  of  further  action ;  and 
when  this  point  is  settled,  test  a  drop  or  two  of  the  clear 
liquid  on  platinum  foil,  to  ascertain  if  anything  has  entered 
into  solution.  If  the  nitric  acid  has  effected  a  partial  solu- 
tion of  the  original  metal,  evaporate  the  liquid  nearly  to  dry- 
ness,  dilute  the  evaporated  mixture  with  water,  filter,  and 
submit  the  nitrate  to  the  usual  course  of  analysis.  The 
residue  is  thoroughly  washed  with  water,  to  prepare  it  for 
further  treatment.  On  diluting  the  evaporated  mixture  with 
water,  a  turbidity  due  to  the  presence  of  bismuth  may  appear. 
The  experienced  operator  will  hardly  fail  to  distinguish  be- 
tween any  such  turbidity  and  a  residue  insoluble  in  the  nitric 
acid.  To  avoid  mistakes  which  would  lead  to  the  unneces- 
sary addition  of  acid,  it  is  well  to  take  out  a  drop  of  the 
nitric  acid  solution  before  evaporation  and  to  add  it  to  sev- 
eral teaspoonfuls  of  water  contained  in  a  test-tube.  (See 
p.  24.)  The  absence  or  presence  of  bismuth  will  thus  be 
discovered.  It  will  sometimes  happen  that  a  white  residue 
appears  in  the  nitric  acid  solution  which  disappears  when  the 
evaporated  mixture  is  diluted.  This  is  owing  to  the  presence 
of  lead  :  nitrate  of  lead  is  rather  insoluble  in  strong  nitric  acid 
but  passes  into  solution  readily  when  the  mixture  is  diluted. 

Three  different  cases  of  insoluble  residues  may  occur, 
readily  distinguished  by  the  mere  appearance  of  the  residue. 

a.  The  insoluble  substance  is  non-metallic  and  white.  In 
this  case  tin  and  antimony  may  be  present,  but  gold  and 


§  96  TEEATMENT  OF  ALLOYS.  123 

platinum  are  probably  absent.  The  white  residue  may  contain 
the  insoluble  oxides  of  tin  and  antimony,  or  either  of  them. 
These  elements  are  to  be  detected  by  the  methods  of  §  25,  or 
by  the  method  described  just  below  (first  part  of  c). 

b.  The  insoluble  substance  is  metallic,  as  evidenced  by  its 
lustre,  if  it  is  in  visible  fragments,  or  by  the  weight  and  gray 
or  black  color  of  its  powder,  if  it  is  in  a  fine  state  of  divi- 
sion. Such  a  residue  must  be  either  gold  or  platinum  (or 
some  of  the  rare  platinum-like  metals  which  lie  without  the 
range  of  this  manual).  The  residue  is  dissolved  in  aqua 
regia,  and  evaporated  to  a  very  small  bulk. 

Test  for  Gold.  —  A  portion  of  this  evaporated  liquid  is 
diluted  with  ten  times  its  bulk  of  water,  and  poured  into  a 
beaker  which  is  placed  on  a  sheet  of  white  paper.  A  small 
quantity  of  a  solution  of  protochloride  of  tin  is  tinged  yellow 
by  the  addition  of  a  few  drops  of  solution  of  sesquichloride 
of  iron  (App.,  §  48),  and  then  considerably  diluted.  A  glass 
rod  is  dipped,  first  into  this  tin  solution,  and  then  into  the 
solution  to  be  tested  for  gold.  If  even  a  trace  of  the  precious 

Test      metal  be  present,  a  blue  or  purple  streak  will  be  ob- 
for       served  in  the  track  of  the  rod.     If  the  quantity  of 

Atu  gold  be  more  considerable  a  pink  tinge  will  be  im- 
parted to  the  solution,  or  a  purplish  precipitate  will  be  pro- 
duced by  a  sufficient  quantity  of  the  tin-solution.  This 
"  purple-of-Cassius "  test  is  applicable  to  very  acid  solu- 
tions. 

Test  for  Platinum.  —  To  another  undiluted  portion  of  the 
cooled  aqua  regia  solution,  a  cold  concentrated  solution  of 
chloride  of  ammonium  is  added.  The  formation  of  a  yellow, 
crystalline  precipitate  of  chloroplatinate  of  ammonium  indi- 

Test     cates  the  presence  of  platinum   (or  of  some  rare 

for      platinum-like  metal).      By  adding  a  little   alcohol 

^*  to  the  liquid,  the  test  is  made  more  delicate.  In  a 
difficult  case,  the  aqua  regia  solution  might  be  evaporated  to 
dryness  with  chloride  of  ammonium,  and  the  residue  treated 
with  weak  alcohol  and  water,  which  would  dissolve  all  the 


124  TREATMENT  OF  ALLOTS.  §  96 

ingredients  except  the  chloroplatiuate.  Upon  ignition,  chloro- 
platinate  of  ammonium  leaves  spongy  platinum  behind. 

It  happens  exceptionally  in  the  case  of  certain  alloys, 
especially  in  the  presence  of  copper,  that  concentrated  nitric 
acid  fails  to  attack  them  even  when  it  is  hot;  it  is  well, 
therefore,  before  inferring  the  presence  of  an  insoluble  me- 
tallic residue  to  try  the  effect  of  boiling  the  seemingty  insol- 
uble substance  in  nitric  acid  diluted  with  an  equal  bulk  of 
water. 

c.  The  insoluble  residue  contains  both  a  white  powder  and 
a  metallic  substance.  It  must  then  be  examined  for  anti- 
mony, tin,  gold  and  platinum.  The  following  directions 
presuppose  the  presence  of  all  four  metals,  —  a  very  rare 
case. 

The  residue  is  treated  for  the  detection  of  antimony  and 
tin,  precisely  as  described  in  §  25.  Gold  and  platinum 
remain  unchanged  in  the  metallic  state  through  the  various 
operations.  After  dissolving  the  tin  in  chlorhydric  acid 
(page  34,  top),  the  residue  is  treated  again  with  chlorhydric 
acid  to  insure  the  complete  removal  of  the  tin,  and  is  then 
washed  thoroughly  by  decantation.  The  washed  residue  is 
warmed  for  a  quarter  of  an  hour  with  a  solution  of  tartaric 
acid  (App.,  §  13),  and  a  few  drops  of  nitric  acid  are  added 
towards  the  close  of  the  digestion.  Antimony  dissolves  in 
this  tartaric  acid  solution ;  its  presence  may  be  verified  by 
passing  sulphuretted  hydrogen  through  the  decanted  solution. 
The  platinum  foil  having  been  taken  out  of  the  porcelain 
dish,  the  metallic  residue  from  the  tartaric  acid  solution  is 
thoroughly  washed  by  decantation,  dissolved  in  aqua  regia, 
and  tested  for  gold  and  platinum,  as  just  described  in  6, 
above. 


§§  97,  98  TREATMENT  OF  LIQUIDS.  125 


CHAPTER  XIII. 
TKEATMENT  OF  LIQUIDS. 

97.  Evaporation  Test.  —  The  first  step  in  the  examina- 
tion of  an  unknown  liquid  is  to  evaporate  a  few  drops  at  a 
gentle  heat  on  platinum  foil.     Attention  should  be  paid  to 
the  smell  of  the  escaping  vapors  in  order  to  ascertain  if  the 
solvent  be  water  or  some  other  fluid,  like  alcohol,  ether,  ben- 
zine, or  a  strong  acid.     If  no  appreciable  residue  remain,  the 
fluid  is  probably  pure  water,  or  some  other  volatile  liquid ; 
or  it  is  possible  that  the  liquid  is  some  very  dilute  solution, 
like  a  spring  water,  which  needs  extreme  concentration  before 
the  solid  substances  dissolved  in  it  can  be  detected.     When 
a  residue  remains  on  the  foil,  the  heat  is  increased,  first,  to 
ascertain  if  the  dissolved  subtances  are  wholly  volatile,  in 
which  case  only  compounds  of  ammonium,  mercury,  arsenic 
and  antimony,  can  be  present ;  and,  secondly,  to  ascertain  if 
there  be  any  organic  matter  in  the  liquid.     Carbonization 
or  charring  with  the  attendant  phenomena  (§  80,  I)  occurs 
when  fixed  organic  matter  is  present.     If  organic  matter  is 
discovered,  it  must  be  destroyed  by  the  second  method  of 
§  82,   before  the  analysis  can  be  proceeded  with.      A   vol- 
atile organic  solvent  can,  of  course,  be  got  rid  of  by  a  simple 
evaporation  to  dryness. 

98.  Testing  with  Litmus.  —  The  next  step  is  to  test 
the  solution  with  litmus-paper. 

a.  If  it  is  neutral,  and  the  solvent  is  water,  consult  §  86. 

b.  If  it  is  acid,  the  acidity  may  be  due  to  a  normal  salt 
having  an  acid  reaction,  or  to  an  acid  salt,  or  to  free  acid. 
No  general  inferences  can  be  drawn  from  the  acid  reaction, 
except  that  carbonates  and  sulphides  are  absent.     If  dilution 


126  TREATMENT  OF  LIQUIDS.  §§  99,  1QO 

of  the  acid  fluid  produces  turbidity,  the  presence  of  antimony 
or  bismuth  may  be  inferred. 

c.     If  it  is  alkaline,  consult  §  85,  c. 

99.  By  evaporating  a  portion  of  the  original  solution  to 
dry  ness,  the  dissolved  solid  is   obtained.     This   solid  may 
be   subjected    to   the   whole   of   the   preliminary   treatment 
prescribed   for  a  salt,  mineral,  or  other  non-metallic  solid 
(§§  80,  81)  ;  but  inasmuch  as  the  main  object  of  all  prelim- 
inary treatment  of  a  solid  is  to  learn  how  to  get  it  into 
solution  with  the  least  difficulty,  it  is  seldom  worth  while  for 
the  analyst  to  make  a  solid  out  of  a  solution,  and  thus  forego 
the  advantage  of  having  the  solution  already  made  to  his 
hand. 

100.  Testing  for  Ammonia.  —  A  small  portion  of  the 
original  solution  must  always  be  tested  for  ammonium  salts, 
by  heating  it  in  a  test-tube  with  an  equal  bulk  of  slaked  lime. 
The  gas  is  recognized  by  its  smell  and  its  reaction  with 
chlorhydric  acid  (§  80,  III.  6). 


The  means  of  identifying  and  isolating  the  rare  elements, 
the  methods  by  which  minute  traces  of  one  substance  may  be 
detected  when  hidden  in  proportionally  large  quantities  of 
other  substances,  as  when  the  impurities  of  chemicals  and 
drugs  are  exhibited,  and  the  processes  to  be  employed  in 
special  cases  of  peculiar  difficulty,  such  as  the  analysis  of 
complex  insoluble  minerals,  or  the  detection  of  mineral  poi- 
sons in  masses  of  organic  matter,  must  be  studied  in  com- 
plete treatises  upon  chemical  analysis,  or  in  works  specially 
devoted  to  these  technical  matters.  Such  details,  however 
valuable  to  the  professional  analyst,  or  expert,  would  not  be 
in  harmony  with  the  plan  of  this  manual. 


APPENDIX. 


BEAGKENTS. 

[**  Those  reagents  in  the  following  list,  which  are  marked  with  the  double 
asterisk,  are  rarely  employed;  a  single,  small  bottle  of  each  of  them  in  the  labora- 
tory, will  be  enough  for  many  students.  *  Those  marked  with  a  single  asterisk 
had  also  better  be  kept  in  one  or  two  bottles  of  sufficient  size,  rather  than  be  dis- 
tributed to  each  student,  because  of  their  liability  to  spoil ;  several  of  them  are  used 
in  considerable  quantities.] 

1.  Chlorhydric  Acid  (Concentrated).— The  strong  common 
acid  prepared  by  chemical  manufacturers,  though  usually  far  from 
pure,  will  answer  for  most  of  the  purposes  of  this  manual.    It  must, 
however,  be  continually  borne  in  mind  that  the  commercial  acid  is 
usually  contaminated  with  sulphuric  acid,  and  very  often  with  traces 
of  arsenic  and  iron.     These  impurities  may  be  present  in  sufficient 
quantity  to  render  the  acid  unfit  for  use  when  these  very  substances 
are  to  be  tested  for  in  the  mixture  to  be  analyzed. 

The  yellow  color  of  the  commercial  acid,  though  often  attributed 
to  iron,  is  really  due  for  the  most  part  to  the  presence  of  a  peculiar 
organic  compound  which  is  soluble  in  the  •strong  acid. 

If  in  any  experiment  doubts  arise  concerning  the  character  of  a 
reagent,  a  quantity  of  it,  somewhat  larger  than  that  which  has  been 
mixed  with  the  substance  under  examination,  should  be  tested  by 
itself,  and  the  reaction  compared  with  that  exhibited  in  the  doubt- 
ful case.  If  the  result  of  this  trial  is  unsatisfactory,  the  experiment 
must  be  repeated  with  reagents  which  are  known  to  be  pure. 

2.  **  Chlorhydric  Acid  (Pure)  may  be  prepared  by  distil- 
ling a  mixture  of  fused  chloride  of  sodium  and  sulphuric  acid,  and 
collecting  the  gas  in  water.    (See  Eliot  and  Storer's  Manual  of  Inor- 
ganic Chemistry,  Exp.  49.) 

3.  Chlorhydric  Acid  (Dilute).  — Mix  1  volume  of  the  com- 


ii  REAGENTS.  §§  4-13 

mon  concentrated  acid,  or  —  where  special  purity  is  required  —  of 
the  pure  strong  acid,  with  4  volumes  of  water. 

4.  Nitric  Acid  (Concentrated). —  Use  the  colorless  commer- 
cial acid  of  1.38  or  1.40  specific  gravity.     Strong  nitric  acid  of  toler- 
able purity  can  usually  be  obtained  from  the  dealers  in  coarse 
chemicals.     An  acid,  which  when  diluted  with  five  parts  of  water 
gives  no  decided  cloudiness  with  either  nitrate  of  silver  (absence  of 
chlorhydric  acid)  or  nitrate  of  barium  (absence  of  sulphuric  acid)  is 
good  enough  for  most  uses  in  qualitative  analysis. 

5.  Nitric  Acid  (Dilute).  —  Mix  1  volume  of  the  strong  acid 
with  5  volumes  of  water. 

6.  Aqua  regia  should  be  prepared  only  in  small  quantities,  at 
the  moment  of  use,  by  mixing  in  a  test-tube  one  volume  of  strong 
nitric  acid,  with  three  or  four  times  as  much  strong  chlorhydric 
acid. 

7,  Sulphuric  Acid  (Concentrated).  — The  oil  of  vitriol  of 
commerce  will  usually  be  found  pure  enough  for  the  purposes  of  this 
manual. 

8,  **  Sulphuric  Acid  (Pure).  — Sulphuric  acid  free  from 
chlorhydric  acid  is  necessary  in  testing  for  chlorine  according  to 
§    71.    Such  acid  may  be  obtained  from  the  dealers  in  fine  chem- 
icals, but  acid  purporting  to  be  pure  should  invariably  be  tested 
by  diluting  a  portion  with  a  considerable  quantity  of  water  and  add- 
ing a  few  drops  of  nitrate  of  silver.    No  turbidity  should  appear 
after  the  mixture  has  stood  for  some  time. 

9,  Sulphuric  Acid  (Dilute)  is  prepared  by  gradually  add- 
ing 1  part  by  measure  of  the  concentrated  acid  to  4  parts  of  water 
contained  in  a  beaker  or  porcelain  dish ;  the  mixture  must  be  con- 
stantly stirred  with  a  glass  rod.     When  the  mixing  is  finished,  the 
liquid  is  left  at  rest  until  all  the  sulphate  of  lead,  which  has  sepa- 
rated from  the  strong  acid,  has  settled  to  the  bottom;  the  clear 
liquid  is  then  decanted  into  bottles. 

**  10.  Sulphuric  Acid  (Dilute)  for  the  separation  of  cop- 
per and  cadmium  (p.  25).  Mix,  as  described  in  the  preceding  sec- 
tion, 1  part  of  the  'strong  acid  with  5  parts  of  water. 

11.  Oxalic  Acid.  —  Dissolve  1  part,  by  weight,  of  the  commer- 
cial crystals,  in  20  parts  of  water. 

12.  Acetic  Acid.  — The  ordinary  commercial  acid. 

13.  Tartaric  Acid  should  be  kept  in  the  state  of  powder,  since 
solutions  of  it  slowly  decompose.    For  use,  dissolve  a  small  portion 
of  the  powder  in  two  or  three  times  its  volume  of  hot  water. 


§§  14-18  REAGENTS.  iii 

14.  Sulphuretted  Hydrogen  Gas  (Sulphydric  Acid),  is 

prepared  as  needed,  by  acting  upon  fragments  of  sulphide  of  iron 
with  dilute  sulphuric  acid  in  the  apparatus  described  in  §§  89,  90  of 
this  Appendix.  The  apparatus  should  always  be  placed  either  in  the 
open  air,  or  in  a  strong  draught  beneath  a  chimney. 

15.  Sulphuretted  Hydrogen  Water.  — Pass  sulphuretted 
hydrogen  gas  into  a  bottle  of  water  until  the  water  can  absorb  no 
more.     To  determine  when  the  absorption  is  complete,  close  the 
mouth  of  the  bottle  tightly  with  the  thumb,  and  shake  the  liquid. 
If  the  water  is  saturated,  a  small  portion  of  the  gas  will  be  set  free 
by  the  agitation,  and  a  slight  outward  pressure  against  the  thumb 
will  be  felt.    If  the  water  is  not  fully  saturated,  the  agitation  will 
enable  it  to  absorb  the  gas  which  lay  in  the  upper  part  of  the  bottle, 
and  a  partial  vacuum  will  be  created,  so  that  an  inward  pressure 
will  be  felt. 

Since  sulphuretted  hydrogen  water  soon  decomposes  when  ex- 
posed to  the  air,  it  should  always  be  kept  in  tightly  closed  bottles, 
and  no  very  large  quantity  of  it  should  be  prepared  at  once.  A  good 
way  of  keeping  the  solution  is  to  fill  a  number  of  small  phials  with 
the  fresh  liquid,  cork  them  tightly,  and  invert  them  in  water,  so 
that  their  necks  shall  always  be  immersed  and  protected  from  the 
atmosphere. 

At  the  moment  of  using  this  reagent  its  quality  should  always  be 
proved  by  smeDing  of  it,  or  by  adding  a  drop  or  two  of  the  liquid  to 
a  drop  of  acetate  of  lead,  which  should  be  immediately  blackened 
from  the  formation  of  sulphide  of  lead. 

16.  Ammonia- Water.  —  Commercial  aqua-ammoniae  may  usu- 
ally be  obtained  pure  enough  for  the  purposes  of  this  manual.   Dilute 
1  volume  of  the  strong  liquor  with  3  volumes  of  water.    Ammonia- 
water  should  be  free  from  carbonic  acid ;  when  diluted,  as  above,  it 
ought  not  to  yield  any  precipitate  when  tested  with  lime-water. 

17.  *  Sulphydrate  of  Ammonium.— Pass  sulphuretted  hydro- 
gen gas  through  ammonia-water,  diluted  as  described  in  §  16,  until  a 
portion  of  the  liquid  yields  no  precipitate  when  tested  with  a  drop 
of  a  solution  of  sulphate  of  magnesium  (absence  of  free  ammonia). 

Since  sulphydrate  of  ammonium  decomposes  after  a  while,  when 
exposed  to  the  air,  it  is  not  advisable  to  prepare  it  in  large  quanti- 
ties. In  case  any  doubt  arise  as  to  the  quality  of  the  reagent,  add 
some  of  it  to  a  drop  of  acetate  of  lead.  Unless  a  dense  black  pre- 
cipitate of  sulphide  of  lead  is  immediately  thrown  down,  the  sulphy- 
drate is  worthless. 

18.  Carbonate  of  Ammonium.  —  Dissolve  1  part,  by  weight, 


iy  REAGENTS.  v       §§  19^22 

of  the  commercial  salt,  in  4  parts  of  water,  and  add  to  the  mixture 
1  part  of  strong  ammonia- water. 

The  solution  of  carbonate  of  ammonium  should  be  kept  in  bottles 
made  of  glass  which  is  free  from  lead.  If  kept  in  flint-glass  bottles, 
the  carbonate  of  ammonium  takes  up  some  lead  so  that  when,  in 
precipitating  the  carbonates  of  Class  VI,  this  reagent  is  added  to  a 
solution  containing  sulphydrate  of  ammonium,  a  dark  coloration 
appears  in  the  liquid  or  obscures  the  precipitate  to  the  annoyance  of 
the  operator. 

10.  Chloride  of  Ammonium. —  Dissolve  1  part,  by  weight,  of 
the  crystallized  commercial  salt  in  10  parts  of  water. 

20.  Oxalate  of  Ammonium.  —  Dissolve  1  part,  by  weight,  of 
the  salt  in  24  parts  of  water:  or,  dissolve  37  grms.  of  crystallized 
oxalic  acid  in  450  c.  c.  of  water,  neutralize,  exactly  with  ammonia- 
water  and  dilute  to  the  bulk  of  1  litre. 

21.  **  Molybdate  of  Ammonium. —  Digest  1  part,  by  weight, 
of  molybdic  acid  for  some  hours  in  4  or  5  parts  of  strong  ammonia- 
water,  and  mix  the  clear  solution  with  12  or  15  parts  of  strong  nitric 
acid ;  or  dissolve  1  part  of  molybdate  of  ammonium  in  3  or  4  parts 
of  weak  ammonia- water,  and  mix  the  liquid  with  12  or  15  parts  of 
nitric  acid,  as  before. 

22.  Caustic  Soda.  —  Place  1  part,  by  weight,  of  the  best  com- 
mercial caustic  soda  in  a  large,  stoppered  bottle ;  pour  upon  it  8  or  9 
parts  of  water,  and  shake  the  bottle  at  intervals  until  the  whole  of 
the  soda  has  dissolved.    Leave  the  bottle  at  rest  until  the  liquid  has 
become  clear,  and  finally  transfer  the  solution,  with  a  siphon,  to  the 
small  bottles  in  which  it  is  to  be  kept  for  use.    The  solution  thus 
prepared,  though  pure  enough  for  the  uses  prescribed  in  this  man- 
ual, is  really  far  from  pure.    It  would  be  unfit  for  use  in  a  delicate 
research,  because  it  is  usually  contaminated  with  chloride,  sulphate 
and  carbonate  of  sodium,  and  is  liable  to  contain  traces  of  alumi- 
nate,  phosphate  and  silicate  of  sodium.     Since  some  nitrate   of 
sodium  is  added  to  it  in  the  process  of  manufacture,  the  soda  is  lia- 
ble to  be  contaminated  with  this  salt  and  the  products  of  its  decom- 
position, including  ammonia.    This  last  impurity  is  liable  to  be  given 
off  when  the  solution  is  boiled. 

Caustic  potash,  as  prepared  for  surgeon's  use,  may  be  substituted 
for  caustic  soda  whenever  it  can  be  more  readily  obtained.  The 
potash  should  be  dissolved  in  about  10  parts  of  water. 

Since  solutions  of  the  caustic  alkalies  act  upon  glass  rather  easily, 
especially  when  its  outer  surface  or  "fire-glaze"  has  once  been  re- 
moved, it  often  happens,  when  the  soda  solution  is  kept  in  glass- 


§§23-30  KEAGENTS.  V 

Btoppered  bottles,  that  the  stoppers  become  immovably  cemented  to 
the  glass  by.  the  silicate  of  sodium  which  forms  in  their  necks.  This 
difficulty  may  be  avoided  by  wiping  the  necks  of  the  bottles  dry  after 
any  of  the  solution  has  been  poured  from  them ;  but  it  will  usually 
be  found  more  convenient  to  replace  the  glass  stoppers  with  plugs 
of  vulcanized  caoutchouc,  or  better  still,  with  small  glass  stoppers, 
over  the  bodies  of  which  short  pieces  of  caoutchouc  tubing  have 
been  stretched.  Solutions  of  the  caustic  alkalies  should  be  kept  in 
bottles  made  of  glass  which  is  free  from  lead. 

23.  Sulphydrate  of  Sodium.  —  Dissolve  1  part  by  weight  of 
commercial  sulphide  of  sodium,  if  it  can  be  obtained,  in  8  parts  of 
water.     Sulphide  of  sodium  may  be  made  by  meltiug  together  in 
an  iron  pot  or  ladle  a  mixture  of  dry  carbonate  of  sodium  with  an 
equal  weight  of  sulphur.    This  operation  does  not  require  a  great 
deal  of  heat  and  it  may  be  performed  over  the  blast  lamp  or  over 
an  ordinary  coal  fire.     Sulphide  of  potassium  is  not  an  available 
substitute  for  sulphide  of  sodium. 

24.  Carbonate  of  Sodium.  —  For  most  purposes  it  is  essen- 
tial that  the  carbonate  of  sodium  should  be  from  sulphate  of  sodium. 
Pure  dry  carbonate  may  be  obtained  from  the  dealers  in  fine  chemi- 
cals or  it  may  be  prepared  by  washing  a  pound  or  two  of  bicarbonate 
of  sodium  repeatedly,  upon  a  filter,  with  small  quantities  of  ice-cold 
water,  until  the  original  quantity  is  reduced  to  a  fifth  or  a  sixth  of  its 
bulk.    The  powder  is  then  dried,  ignited,  and  kept  in  well-stoppered 
bottles. 

25.  Biborate  of  Sodium.  —  Common  borax,  powdered, 

26.  Phosphate  of  Sodium.  —  Dissolve  1  part,  by  weight,  of 
"  common  phosphate  of  soda"  in  10  parts  of  water. 

27.  Acetate  of  Sodium.  —  Dissolve  1  part  of  the  crystallized 
salt  in  10  parts  of  water. 

23.    Nitrate  of  Sodium.  —  Select  a  clean  white  sample  of  the 
commercial  salt  and  keep  in  the  form  of  a  coarse  powder. 

29,  **Acid  Sulphate  of  Sodium.  —  Heat  a  mixture  of  16 
parts,  by  weight,  of  Glauber's  salt,  and  5  parts  of  concentrated  sul- 
phuric acid,  in  a  platinum  vessel,  until  a  portion  of  the  melted  mass 
becomes  distinctly  solid  when  taken  up  on  a  glass  rod.    Then  allow 
the  mixture  to  become  cold ;  remove  the  cold  lump  from  the  plati- 
num vessel,  and  break  it  into  fragments.    Keep  the  coarse  powder 
in  a  tight,  glass-stoppered  bottle. 

30.  Sulphate  of  Potassium.  —  Dissolve  one  part,  by  weight, 
of  the  crystallized  salt  in  200  parts  of  water.    A  solution  of  this 


vi  EEAGENTS.  §§31-37 

strength  contains  the  same  proportional  quantity  of  sulphuric  acid 
as  is  contained  in  a  saturated  aqueous  solution  of  sulphate  of  cal- 
cium. Hence  it  cannot  precipitate  the  latter  when  added  to  solu- 
tions of  the  soluble  calcium  salts. 

31.  Chromate  of  Potassium.  —  (The  normal  or  "neutral" 
yellow  chromate.)     Dissolve  1  part,  by  weight,  of  the  salt  in  8  parts 
of  water. 

32.  Bichromate  of  Potassium.  —  The  pure  crystallized  salt 
is  kept  in  the  form  of  powder.    It  must  be  entirely  free  from 
chloride. 

33.  Ferrocyanide  of   Potassium.  —  ( Yellow    Prussiate  of 
Potash.)    Dissolve  1  part,  by  weight,  of  the  commercial  salt  in  12 
parts  of  water. 

34.  *  *  Ferricyanide  of  Potassium.  —  (Red   Prussiate  of 
Potash.)     Since  the  aqueous  solution  of  this  salt  undergoes  decom- 
position, with  formation  of  some  ferrocyanide,  when  kept  for  any 
length  of  time,  the  salt  should  be  kept  for  use  in  the  form  of  pow- 
der.   The  commercial  salt  is  pure  enough  for  analytical  purposes. 
A  minute  fragment  of  it  may  be  dissolved  in  water  at  the  moment 
of  use. 

35.  **  Cyanide  of  Potassium.  —  The  better  sorts  of  the 
commercial  article  are  pure  enough  for  analytical  purposes.     It 
should  be  kept  in  the  solid  form  in  a  tightly  stoppered  bottle. 
When  the  solution  is  required,  dissolve  1  part  of  the  salt  in  4  parts 
of  cold  water. 

36.  Nitrate  of  Potassium.  —  Refined  saltpetre  may  be  em- 
ployed.   It  should  be  kept  in  the  state  of  powder. 

37.  **  Nitrite  of  Potassium.  —  Weigh  out  8  parts  of  concen- 
trated nitric  acid,  mix  it  with  an  equal  weight  of  water,  and  place 
the  mixture  in  a  glass  flask  provided  with  a  perforated  cork  and 
gas  delivery-tube.     The  flask  should  be  so  large  that  the  mixture 
only  half  fills  it.     Throw  into  the  liquid  2  parts  of  starch,  in  lumps, 
and  heat  the  mixture  until  red  fumes  of  nitrous  and  hyponitric  acids 
begin  to  be  given  off;  then  remove  the  lamp  lest  the  action  become 
too  violent.    Conduct  the  fumes  into  a  bottle  containing  5  parts  of 
potash-lye  of  1.27  sp.  gr.,  until  the  latter  is  saturated.     Then  filter 
the  saturated  liquid,  and  evaporate  it  to  dryness.    For  use,  dissolve 
1  part  of  the  dry  salt  in  2  parts  of  water. 

The  nitrite  of  potassium  bought  of  dealers  in  fine  chemicals  is 
often  unfit  for  the  uses  prescribed  in  this  manual ;  it  can  readily  be 


§§  38-47  REAGENTS.  vii 

made  good,  however,  by  dissolving  it  in  twice  its  weight  of  water 
and  saturating  the  solution  with  nitrous  fumes. 

38.  *  Iodide  of  Potassium   and  Starch  Papers. —Dis- 
solve a  gramme  of  pure  iodide  of  potassium  (free  from  iodate)  in 
200  cubic  centimetres  of  water.     Heat  the  solution  moderately  in  a 
porcelain  dish,  and  stir  into  it  ten  grammes  of  starch  which  has 
been  reduced  to  the  consistence  of  cream  by  rubbing  it  in  a  mortar 
with  a  small  quantity  of  water.    Stir  the  mixture  until  it  gelatinizes, 
taking  care  not  to  burn  the  starch,  then  allow  the  paste  to  cool,  and 
spread  it  thinly  upon  one  side  of  white  glazed  paper  with  a  wooden 
spatula.    Dry  the  paper,  cut  it  into  strips  as  large  as  the  little  fin- 
ger and  preserve  it  in  stoppered  bottles  kept  carefully  closed. 

39.  Nitrate  of  Silver.  —  Dissolve  1  part,  by  weight,  of  the 
commercial  crystals  in  20  parts  of  water. 

40.  *  Slaked  Lime.  —  Mix  common  quicklime  with  half  its 
weight  of  water.    Keep  the  powder  in  bottles  with  tight  stoppers. 

41.  *  Lime  "Water.  —  Place  a  handful  of  slaked  lime  in  a  large 
bottle,  pour  in  enough  water  to  almost  fill  the  bottle,  cork  the  latter 
tightly,  and  shake  it  at  intervals  during  several  days.    Decant  the 
clear  liquid  into  smaller  bottles  for  use.     Refill  the  large  supply  - 
bottle  with  water,  and  again  shake  it  at  intervals. 

42.  Chloride  of  Calcium,  —  Stir  powdered  white    marble 
into  dilute  chlorhydric  acid  until  the  acid  is  saturated,  and  dilute  1 
part  of  the  concentrated  solution  with  5  parts  of  water. 

43.  Chloride  of  Barium.  —  Dissolve  1  part,  by  weight,  of 
the  commercial  salt  in  10  parts  of  water. 

44.  **  Nitrate  of  Barium.  —  Dissolve  1  part,  by  weight,  of 
the  commercial  salt  in  15  parts  of  water. 

45.  Acetate  of  Lead.  —  Dissolve  1  part,  by  weight,  of  "  sugar 
of  lead"  in  10  parts  of  water. 

48.  *  Lead  Paper.  —  Wet  strips  of  white  paper  in  a  solution  of 
acetate  of  lead,  or  better,  in  a  solution  of  subacetate  of  lead,  and 
dry  them  in  air  which  is  free  from  sulphuretted  hydrogen.  Cut  the 
dried  paper  into  slips  as  large  as  the  little  finger,  and  keep  the  slips 
in  tightly  stoppered  bottles.  Or,  paper  may  be  slightly  moistened 
with  a  solution  of  acetate  of  lead  at  the  moment  of  use. 

47,  Sulphate  of  Magnesium  and  Chloride  of  Ammo- 
nium. —  Dissolve  24.6  grammes  of  Epsom  salt  and  33  grammes  of 
commercial  chloride  of  ammonium  in  water,  add  some  ammonia- 
water  to  the  solution  and  dilute  the  liquor  to  the  volume  of  a  litre. 
12 


viii  EEAGEXTS.  §§48-56 

If  less  than  a  litre  of  the  reagent  is  required,  the  weights  above 
given  may,  of  course,  be  reduced  in  any  desired  proportion.  Fil- 
ter the  solution  to  separate  any  precipitate  of  ferric  hydrate  or 
other  insoluble  matters,  which  may  have  been  present  as  impurities 
in  the  components  of  the  mixture,  and  preserve  the  clear  liquid. 

From  a  solution  thus  prepared  no  hydrate  of  magnesium  can  be 
precipitated  by  ammonia-water ;  herein  consists  the  advantage  of 
the  mixture  as  a  test  for  phosphoric  and  arsenic  acids. 

48.  **  Ferric  Chloride.  —  This  solution  is  prepared  bypass- 
ing chlorine  gas  through  a  saturated  solution  of  iron  tacks  in 
chlorhydric  acid,  until  a  drop  of  the  fluid  no  longer  produces  a  blue 
precipitate  in  a  solution  of  ferricyanide  of  potassium.    The  solu- 
tion is  then  heated  to  expel  the  excess  of  chlorine. 

49.  ** Nitrate  of  Cobalt,  —Dissolve  1  part,  by  weight,  of 
the  crystallized  salt  in  10  parts  of  water. 

50.  **  Sulphate  of  Copper.  —  Dissolve  1  part,  by  weight,  of 
the  crystallized  salt  (blue  vitriol)  in  10  parts  of  water. 

51.  **  Protochloride  of  Tin.  —  This  solution  is  prepared  by 
boiling  scraps  of  tin  with  strong  chlorhydric  acid  until  hydrogen 
ceases  to  be  evolved.    The  tin  must  be  in  excess.     The  solution  is 
diluted  with  four  times  its  bulk  of  water  acidulated  with  chlorhydric 
acid,  and  filtered,  if  necessary.     The  clear  liquid  must  be  kept  in  a 
tightly  closed  bottle  containing  some  bits  of  tin. 

52.  **  Black  Oxide  of  Manganese.  —  The  artificially  pre- 
pared pure  binoxide  of  manganese. 

53.  **  Bed  Oxide  of  Mercury.  —  The  commercial  oxide.    It 
should  leave  no  residue  when  heated  upon  platinum  foil. 

54.  **  Chloride  of  Mercury.  —  Dissolve  1  part  of  "corro- 
sive sublimate"  in  16  parts  of  water. 

55.  **  Bichloride  of  Platinum.  —  Cut  a  small  quantity  of 
-^orn-out  platinum  foil  into  very  fine  pieces  and  boil  them  in  a  porce- 
lain dish,  with  successive  small  portions  of  aqua  regia  until  all  the 
metal  has  been  dissolved.     Collect  the  several  portions  of  aqua  regia, 
partially  saturated  with  platinum,  in  another  dish,  and  evaporate  the 
liquid  to  dryness  on  a  water  bath.    Dissolve  the  residue  in  10  parts 
of  water  for  use. 

56.  Zinc.  —  The  commercial  sheet  metal,  although  usually  con- 
taminated with   lead    and    cadmium  and    often    containing  faint 
traces  of  arsenic  and  sulphur,  will  generally  be  found  pure  enough 
for  the  purposes  of  this  manual. 


§§57-61  KEAGENTS.  ix 

57.  **"  Solution  of  Indigo"  (Sulphindigotic  Acid).— 

Pour  5  parts  (5  grammes  will  be  ample)  of  fuming  sulphuric  acid 
into  a  beaker,  place  the  latter  in  a  dish  of  water  to  keep  it  cool,  and 
stir  into  the  acid,  little  by  little,  1  part  of  finely  powdered  indigo. 
When  all  the  indigo  has  been  added  to  the  acid,  leave  the  mixture  at 
rest  for  48  hours ;  then  pour  it  into  20  times  its  own  volume  of 
water,  filter  the  mixture  and  preserve  the  filtrate  for  use.  Instead 
of  6  parts  of  fuming  sulphuric  acid,  12  or  14  parts  of  the  ordinary 
strong  acid  may  be  employed ;  in  this  case,  however,  the  mixture 
must  be  heated  for  several  hours  on  a  water-bath. 

58.  Litmus  Paper.  — Heat  1  part,  by  weight,  of  commercial 
litmus  with  6  parts  of  water,  upon  a  water  bath  for  several  hours, 
taking  care  to  replace  the  water  which  evaporates.    Filter,  divide 
the  filtrate  into  two  equal  portions,  and  stir  one  half  repeatedly 
with  a  glass  rod  dipped  in  very  dilute  nitric  acid,  until  the  color 
appears  distinctly  red.     Pour  the  blue  and  red  halves  into  a  porce- 
lain dish,  and  stir  the  mixture.    Draw  strips  of  fine  unsized  paper 
through  the  liquid,  and  hang  them  on  cords  to  dry.    The  color  of 
the  paper  thus  obtained  is  not  blue  but  bluish-violet.    It  turns  blue 
when  touched  with  an  alkali,  and  red  when  exposed  to  acids,  and 
may  be  used  indifferently  as  a  test  for  either  acids  or  alkalies. 

59.  Starch  Paste  should  be  prepared,  when  wanted  for  use, 
by  boiling  30  cubic  centimetres  of  water  in  a  porcelain  dish,  and 
stirring  into  it  half  a  gramme  of  starch  which  has  previously  been 
reduced  to  the  consistence  of  cream  by  rubbing  it  in  a  mortar  with 
a  few  drops  of  water. 

60.  *  Alcohol.  —  Common  alcohol  of  85  or  90  per  cent. 

61.  "Water.  —  Clean  rain  water  will  serve  well  enough  for  most 
of  the  purposes  of  this  manual.     In  granitic  regions  the  water  of 
many  lakes,  brooks  and  ponds  also  is  nearly  pure.    Pure  water  may 
be  obtained  by  melting  blocks  of  compact  ice,  or  by  distilling  ordi- 
nary water  in  glass  or  copper  retorts  and  rejecting  the  first  portions 
of  the  distillate.    It  should  yield  no  precipitate  when  tested  with 
chloride  of  barium  and  nitrate  of  silver. 


§62 


SOLUTIONS  OP  KNOWN  COMPOSITION. 

62.  In  case  the  experiments  indicated  in  Part  I  are  to  be  per- 
formed by  a  considerable  number  of  students,  it  will  be  found  con- 
venient to  prepare  beforehand  a  moderate  supply  of  the  various 
solutions  required  in  making  the  known  mixtures  under  the  several 
classes.  These  solutions  may  be  made  of  the  strengths  indicated 
below. 

Chloride  of  Copper. — Dissolve  black  oxide  of  copper  in  5 
times  its  weight  of  a  mixture  of  equal  parts  of  strong  chlorhydric 
acid  and  water.  Dilute  the  resulting  solution  with  3  times  its  bulk 
of  water.  [A  single  student  in  performing  the  experiment,  may  dis- 
solve a  few  grains  of  the  oxide  in  a  small  quantity  of  the  strong 
acid,  and,  in  general,  may  make  the  solutions  as  needed  for  use  by 
taking  a  crystal  or  a  small  amount  of  the  required  substance  in 
powder,  as  the  case  may  be,  without  regard  to  the  exact  amount.  It 
is  well,  however,  not  to  start  with  such  quantities  as  to  make  the 
precipitates  inconveniently  bulky.] 

Arsenious  Acid.  —  Dilute  a  quantity  of  chlorhydric  acid  with 
half  its  bulk  of  water  and  saturate  it  with  arsenious  acid  at  a  gentle 
heat.  When  the  solution  has  become  cold,  pour  off  the  clear  liquor 
from  the  arsenious  acid  which  has  crystallized  out. 

Ferrous  Chloride.  —  Treat  warm  dilute  chlorhydric  acid  (App., 
§  3)  with  as  much  iron  (wire  or  filings)  as  it  will  dissolve  and  then 
dilute  the  solution  with  an  equal  bulk  of  water.  [This  solution 
should  be  prepared  only  in  small  quantity  and  kept  in  a  well-siop- 
pered  bottle.] 

Chloride  of  Zinc. — To  a  quantity  of  chlorhydric  acid  diluted 
with  an  equal  bulk  of  water,  add  as  much  zinc  as  the  acid  will  dis- 
solve and  then  add  to  the  solution  5  times  its  bulk  of  water. 

Chloride  of  Calcium.  —  Stir  powdered  white  marble  or  chalk 
into  chlorhydric  acid  diluted  with  twice  its  bulk  of  water  until  the 
acid  is  saturated ;  filter  the  solution  if  necessary. 

Chloride  of  Magnesium.  —  Add  "magnesia  alba"  to  dilute 
chlorhydric  acid  until  the  acid  is  saturated,  then  dilute  the  solution 
with  twice  its  bulk  of  water. ' 

Chloride  of  Sodium.  —  Dissolve  common  salt  in  10  times  its 
weight  of  water. 


§  62  KNOWN  SOLUTIONS.  xi 

Nitrate  of  Silver.  —  Dissolve  the  crystallized  salt  in  10  times 
its  weight  of  water. 

Mercurous  Nitrate,  —  Dilute  a  small  quantity  of  strong  nitric 
acid  with  an  equal  bulk  of  water,  and  to  the  mixture,  warmed  over 
the  lamp,  add  more  mercury  than  will  dissolve.  When  action  has 
ceased  dilute  the  solution  with  5  times  its  bulk  of  water  and  keep  in 
a  bottle  containing  a  small  amount  of  metallic  mercury. 

Nitrate  of  Lead.  —  Dissolve  the  crystallized  salt  in  5  times  its- 
weight  of  water. 

Mercuric  Chloride.  —  Dissolve  corrosive  sublimate  in  20  times 
its  weight  of  water. 

Chloride  of  Bismuth.  —  Dissolve  metallic  bismuth  in  aqua 
regia.  When  the  acid  is  saturated  pour  off  the  solution  from  the 
undissolved  metal,  dilute  it  with  twice  its  bulk  of  water  and  add 
strong  chlorhydric  acid  to  dissolve  the  precipitated  oxy-chloride. 
Or,  dissolve  the  commercial  sub-nitrate  in  chlorhydric  acid  and 
dilute  as  before. 

Chloride  of  Cadmium.  —  Dissolve  the  commercial  salt  in  10 
times  its  weight  of  water. 

Chloride  of  Lead.  —  Boil  dilute  chlorhydric  acid  with  an  ex- 
cess of  litharge  and  filter  the  solution  when  perfectly  cold. 

Chloride  of  Antimony,  —  Dilute  the  commercial  strong  solu- 
tion with  an  equal  bulk  of  water  and  add  strong  chlorhydric  acid 
to  dissolve  the  basic  chloride  which  is  precipitated.  Or,  dissolve 
the  finely  powdered  metal  in  aqua  regia  and  dilute  as  before. 

Sulphate  of  Manganese.  —  Dissolve  the  crystallized  salt  in  10 
times  its  weight  of  water. 

Common  Alum.  —  Dissolve  in  10  times  its  weight  of  water. 

Chrome  Alum.  —  Dissolve  in  10  times  its  weight  of  water. 

Bone  Ash  (p.  38)  had  better  be  kept  in  powder  and  dissolved  as 
needed,  in  order  that  the  student  may  not  lose  sight  of  the  fact  that 
this  compound  requires  an  acid  solvent. 

Nitrate  of  Cobalt,  —  Dissolve  in  10  times  its  weight  of  water. 

Nitrate  of  Nickel,  —  Dissolve  in  10  times  its  weight  of  water. 
(The  chlorides  of  nickel  and  cobalt  answer  equally  well  and  the 
solutions  maybe  made  of  the  same  strength.) 

Chloride  of  Barium.  —  Dissolve  the  crystallized  salt  in  5  times 
its  weight  of  water. 

Chloride  of  Strontium.  —  Dissolve  the  crystallized  salt  in  5 
times  its  weight  of  water.  (The  nitrate  will  answer  equally  well.) 


xii  KNOWN  SOLUTIONS.— UTENSILS.  §  63 

Nitrate  of  Potassium.  —  Dissolve  1  part  of  the  commercial 
salt  in  5  parts  of  water. 

Sulphate  of  Sodium.  —  Dissolve  1  part  of  Glauber's  salt  in  10 
parts  of  water. 

Phosphate  of  Sodium.  —  Dissolve  commercial  "  phosphate  of 
soda"  in  10  parts  of  water  as  in  App.,  §  26. 

Carbonate  of  Sodium.  —  Dissolve  1  part  of  "  sal  soda"  in  5 
parts  of  water. 

Oxalate  of  Potassium.  —  Dissolve  1  part  of  the  crystallized 
salt  in  5  parts  of  water. 

Tartrate  of  Potassium.  —  Dissolve  tartaric  acid  in  5  times  its 
weight  of  water  and  neutralize  it  exactly  with  carbonate  of  potas- 
sium. 

Iodide  of  Potassium.  —  Dissolve  1  part  of  the  crystallized 
salt  in  10  parts  of  water. 


UTENSILS. 

63.  The  implements  required  by  the  student  of  qualitative 
analysis  are  few  and  simple.  Besides  bottles  for  the  reagents  enu- 
merated in  the  foregoing  list,  and  a  few  small  phials  for  the  preser- 
vation of  samples  of  salts  and  mixtures  to  be  analyzed,  there  will 
be  needed: — 

A  dozen  test-tubes,  A  wash-bottle, 

A  wooden  test-tube  rack,  2  small  evaporating  dishes, 

A  test-tube  brush,  A  procelain  crucible, 

A  nest  of  small  beakers,  1  triangle  of  iron-wire, 

2  or  3  glass  stirring-rods,  An  iron  ring-stand, 

A  small  thistle-,  or  funnel-tube,  A  filter-stand, 

A  larger  thistle-tube  for  the  gas-  A  lamp, 

generator,  A  gas-bottle  for  generating  sul- 

1  stick  of  No.  7  glass  tubing  (see       phuretted  hydrogen, 

App.,  §  82),  A  common  jeweller's  blowpipe, 

2  or  3  sticks  of  No.  4  glass  tub-    A  pair  of  small  iron  pincers  (jew- 
ing, eller's  tweezers), 

3  small  glass  funnels,  A  piece  of  platinum  foil, 
A  small  glass  flask,                           A  bit  of  platinum  wire, 


§  64  REAGENT  J30TTLES.  xiii 

A  small  platinum  crucible  is  also  A  few  corks  or  caoutchouc  stop- 
very  desirable,  pers, 

A  few  packages  of  cut  filters,  or  a  A  piece  of  blue  cobalt  glass  (see 

quire  of  filter  paper,  §  42). 

64.  Reagent  Bottles.  —  The  bottles  in  which  reagents  are 
kept  should  be  of  cylindrical  shape,  and  rather  high  than  wide. 
They  should  be  closed  with  glass  stoppers  which  fit  accurately,  but 
are  not  very  finely  ground.  The  stoppers  should  have  upright  (not 
mushroom-shaped)  heads.  Most  of  the  liquid  reagents  may  be 
conveniently  kept  in  narrow-mouthed  bottles  of  the  capacity  of  6 
fluid  ounces ;  but  to  avoid  the  necessity  of  frequently  refilling  the 
bottles,  it  is  well  to  keep  the  solutions  most  commonly  employed  — 
namely,  dilute  chlorhydric  and  nitric  acids,  ammonia-water,  chloride 
of  ammonium  and  carbonate  of  ammonium  —  in  8-ounce  bottles. 
Care  must  be  taken  in  this  case  to  choose  bottles  of  such  shape  that 
they  can  be  readily  grasped  between  the  thumb  and  fingers. 

For  the  reagents  which  are  to  be  kept  in  the  dry  state,  wide- 
mouthed  bottles  of  the  capacity  of  2  or  3  ounces  should  be  chosen. 

Reagent  bottles  should  always  be  made  "  extra-heavy,"  since, 
from  constant  use,  they  are  exposed  to  many  blows.  The  lustrous 
"  flint-glass"  bottles  of  American  or  English  make  are  ill  suited  for 
the  preservation  of  liquid  reagents ;  for  such  glass  is  easily  attacked 
by  many  chemical  agents,  and  is  therefore  likely  to  render  the  re- 
agents impure.  German  bottles  are  usually  to  be  preferred.  They 
are  made  of  glass  free  from  lead,  have  round  shoulders  and  well- 
ground  stoppers,  and  are  often  numbered  both  upon  the  bottle  and 
the  stoppers,  so  that  the  proper  place  of  the  latter  can  always  be 
discovered.  French  bottles,  though  made  of  good  glass  and  sold  at 
a  low  price,  have  often  such  square  shoulders  that  it  is  wellnigh  im- 
possible to  empty  them  completely,  and  often  difficult  to  pour  out  a 
liquid  from  them  drop  by  drop.  Their  stoppers,  moreover,  are 
usually  too  finely  ground,  and  are  hence  constantly  liable  to  stick 
fast. 

Each  reagent  bottle  should  be  kept  in  a  particular  place  on  shelves 
before  the  operator  and  convenient  to  his  hand.  Whenever  a  re- 
agent is  to  be  used,  the  bottle  which  contains  it  should  be  grasped  in 
the  right  hand ;  the  stopper  should  be  .taken  out  by  pinching  it  be- 
tween the  first  and  second  or  third  and  fourth  fingers  of  the  left 
hand,  or  by  pressing  it  between  the  little  finger  and  palm  of  that 
hand.  In  either  case,  the  bottle  is  withdrawn  from  the  stopper,  and 
not  the  stopper  from  the  bottle.  Neither  bottle  nor  stopper  should 
be  put  upon  the  table ;  the  stopper  should  be  held  in  the  left  hand 


xiv  TEST-TUBES.  §  (J5 

as  long  as  the  bottle  is  open.  When  the  reagent  has  been  poured 
out,  the  bottle  is  immediately  closed,  and  returned  to  its  place  upon 
the  shelf.  If  these  apparently  trifling  particulars  are  scrupulously 
attended  to,  no  stopper  can  ever  be  misplaced,  or  soiled  by  contact 
with  liquids  or  dirt  on  the  table;  and  the  bottle  will  always  be 
found  in  its  proper  place  when  instinctively  reached  for.  Moreover, 
the  label  on  the  bottle  cannot  be  injured  by  drops  of  the  reagent, 
since  the  liquid  must  necessarily  be  poured  from  the  back,  or  blank 
side  of  the  bottle. 

When  a  stopper  sticks  tightly  in  the  neck  of  a  bottle,  it  may 
sometimes  be  loosened  by  pressing  it  first  upon  one  side,  and  then 
upon  the  other,  with  the  thumb  of  the  right  hand,  while  the  fingers 
of  that  hand  grip  the  bottle,  and  the  bottle  is  held  still  with  the 
left  hand.  Or  the  neck  of  the  bottle  may  be  immersed  in  hot  water 
for  a  minute  or  two,  to  expand  the  glass  outside  the  stopper.  The 
stopper  can  then  usually  be  taken  out  without  trouble.  The  hot 
water  may  be  conveniently  applied  by  pouring  a  slow  stream  of  it 
from  a  wash-bottle  upon  the  neck  of  the  bottle.  Another  way  is 
to  heat  the  neck  of  the  bottle  over  a  very  small  flame  of  the  gas  or 
alcohol  lamp.  No  matter  how  the  glass  is  heated,  the  bottle  must 
be  constantly  turned  round  and  round,  in  order  that  each  side  of 
the  neck  may  be  equally  exposed  to  the  heat  and  the  risk  of  crack- 
ing the  bottle  so  be  lessened. 

65.  Test-tubes  are  little  cylinders  of  thin  glass  with  round 
thin  bottoms  and  lips  slightly  flared.  Their  length  may  be  from  five 
to  seven  inches,  and  their  diameter  from  one  half  to  three  fourths 
of  an  inch ;  they  should  never  be  so  wide  that  the  open  end  cannot 
be  closed  by  the  ball  of  the  thumb. 

Test-tubes  are  used  for  heating  small  quantities  of  liquid  over  the 
gas-  or  spirit-lamp ;  they  may  generally  be  held  by  the  upper  end  in 
the  fingers  without  inconvenience ;  but  in  case  they  become  too  hot 
to  be  held  in  this  way,  a  strip  of  thick  folded  paper  may  be  nipped 
round  the  tube,  and  grasped  between  the  thumb  and  forefinger  just 
outside  the  tube. 

Two  precautions  are  invariably  to  be  observed  in  heating  test- 
tubes  :  —  1st.  The  outside  of  the  tube  must  be  wiped  perfectly  dry ; 
and  2d.  The  tube  must  be  moved  in  and  out  of  the  flame  for  a  min- 
ute or  two  when  first  heated.  It  should  be  rolled  to  and  fro  also  to 
a  slight  extent  between  the  thumb  and  forefinger,  in  order  that  each 
side  of  it  may  be  equally  exposed  to  the  flame.  A  drop  of  water  on 
the  outside  of  the  tube  keeps  one  spot  cooler  than  the  rest.  The 
tube  breaks,  because  its  parts,  being  unequally  heated,  expand  un- 
equally, and  tear  apart. 


§§  66-70 


FLASKS.  —  FILTERING. 


XV 


Pig.  1. 


When  a  liquid  is  boiling  actively  in  a  test-tube,  it  sometimes  hap- 
pens that  portions  of  the  hot  liquid  are  projected  out  of  the  tube 
with  some  force ;  the  tube  should  therefore  always  be  held  in  an  in- 
clined position,  and  the  operator  should  be  careful  not  to  direct  it 
towards  himself,  or  towards  any  other  person  in  his  neighborhood. 

Test-tubes  are  cleaned  by  the  aid  of 
cylindrical  brushes  made  of  bristles  caught 
between  twisted  wires,  like  those  used 
for  cleaning  lamp-chimneys ;  the  brushes 
should  have  a  round  end  of  bristles. 

66.  Test-tube   Rack.  —  Test-tubes 
are  kept  in  a  wooden  rack,  such  as  is  rep- 
resented in  Figure  1.    When  in  use,  the 
tubes  stand  upright  in  the  holes  of  the 

rack;  but  clean  tubes  are  inverted  upon  the  pegs  behind  the  holes, 
in  ordor  that  they  may  be  kept  free  from  dust,  and  that  the  last  por- 
tions of  wash-water  may  drain  away  from  them  after  washing. 
The  rack  should  be  large  enough  to  hold  a  dozen  tubes.  Care 
should  be  taken  that  the  tubes  are  washed  perfectly  clean  before 
being  inverted  on  to  the  pegs  lest  the  pegs  themselves  become  dirty. 

67.  Flasks.  —  Small  Berlin  flasks  of  two  or  three  ounces  capa- 
city are  well  suited  for  the  purposes  of  qualitative  analysis.    These 
German  flasks  are  tough,  capable  of  withstanding  sudden  changes 
of  temperature,  and  durable,  although  their  bottoms  and  sides  have 
all  the  requisite  thinness.     When  a  liquid  is  to  be  boiled  in  a  flask, 
the  flask  should  be  placed  upon  a  support  of  wire-gauze  (App.,  §  70), 
and  sufficiently  inclined  to  prevent  any  particles  of  the  liquid  from 
being  thrown  out  of  the  neck  by  the  movement  of  ebullition. 

As  with  test-tubes  and  all  other  glass  or  porcelain  vessels  of 
whatever  form,  the  outside  of  a  flask  must  be  wiped  perfectly  dry 
before  exposing  it  to  the  lamp.  The  flame  should  be  moved  about 
also  beneath  the  flask,  at  first,  in  order  that  the  temperature  of  the 
latter  may  be  raised  equally  and  not  too  rapidly. 

68.  Beakers  are  thin,  flat-bottomed  tumblers  with  a  slightly 
flaring  rim.    They  are  bought  in  sets  or  nests.    A  nest  in  which 
the  largest  sized  beaker  has  a  capacity  of  about  6  ounces  will  be 
sufficient  for  the  requirements  of  this  work. 

69.  Glass  Funnels  should  be  thin  and  light,  and  should  be 
about  2  or  2.5  inches  in  diameter.    Their  sides  should  incline  at  an 
angle  of  60°.    The  Wider  the  throat  of  the  funnel  the  better. 

70.  Filtering.  —  Paper  filters  are  employed  in  qualitative  analy- 


xvi  FILTERING.  §  70 

sis  to  separate  precipitates  from  the  liquids  in  which  they  have  been 
formed.  A  good  filtering-paper  must  be  porous  enough  to  filter  rap- 
idly, and  yet  sufficiently  close  in  texture  to  retain  the  finest  powders ; 
and  it  must  also  be  strong  enough  to  bear,  when  wet,  the  pressure  of 
the  liquid  which  is  poured  into  upon  it.  Filter-paper  should  never 
contain  any  gypsum  or  other  soluble  material,  and  should  leave  only 
a  small  proportion  of  ash  when  burned.  White  or  light-gray  paper 
is  to  be  preferred  to  colored,  since  it  more  commonly  fulfils  these 
requirements. 

Filteringrpaper  is  commonly  sold  in  sheets,  which  may  be  cut  into 
circles  of  any  desired  diameters  for  use,  according  to  '  the  various 
scales  of  operation,  and  quantities  of  liquids  to  be  filtered.  Or  pack- 
ages of  "  cut-filters  "  may  be  procured  ready-made  from  the  dealers 
in  chemical  wares. 

As  a  general  rule,  small  filters  should  be  employed  in  analytical 
operations;  the  mixture  to  be  filtered  should  be  poured  by  small 
successive  portions  upon  a  filter  no  larger  than  is  needed  to  hold 
the  whole  of  tie  solid  matter  which  is  to  be  col- 
lected.   Filters  abeut  three  inches  in  diameter  are 
well  suited  for  most  of  the  analytical  operations 
described  in  this  work,  though  there  are  many 
cases  where  smaller  filters  are  required,  and  a  few 
instances  in  which  filters  as  large  as  four  inches 
in  diameter  might  be  necessary. 

There  are  two  ready  methods  of  preparing  filters 
for  use.     According  to  the  first  method,  shown  in 
Fig.  2,  a  circle  of  paper  is  folded  over  on  its  own 
diameter,    and  the   semicircle   thus    obtained  is 
folded  once  upon  itself  into  the  form  of  a  quadrant ;  the  paper  thus 
folded  is  opened  so  that  three  thicknesses  shall  come  upon  one  side, 
and  one  thickness  upon  the  other,  as  shown  in  the  upper  half  of 
Fig.  2;  the  filter  is  then  placed  in  a  glass  funnel,  the  angle  of  which 
should  be  precisely  that  of  the  opened  paper,  viz., 
Pig.  3.  60°.    The  paper  may  be  so  folded  as  to  fit  a  funnel 

whose  angle  is  more  or  less  than  60°,  but  this  is  the 
most  advantageous  angle,  and  funnels  should  be 
selected  with  reference  to  their  correctness  in  this 
respect. 

In  the  second  method  of  folding  filters,  the  circle 
of  paper  is  doubled  once  upon  itself  as  before  into 
the  form  of  a  semicircle,  and  a  fold  equal  to  one 
quarter  of  this  semicircle  is  turned  down  on  each 
side  of  the  paper.  Each  of  the  quarter  semicircles 
is  then  folded  back  upon  itself,  as  shown  in  the  lower  half  of  Fig.  3 ; 


§71 


FILTERING. 


XVll 


the  filter  is  opened,  without  disturbing  the  folded  portions,  and 
placed  in  the  funnel.  Filtration  can  be  rapidly  effected  with  this 
kind  of  filters,  for  the  projecting  folds  keep  open  passages  between 
the  filter  and  the  funnel,  and  thus  facilitate  the  passage  of  the  liquid. 
That  portion  of  the  circle  of  paper,  which  must  necessarily  be 
folded  up  in  order  to  give  the  requisite  conical  form  to  a  paper 
filter,  retards  filtration  in  the  first  manner  of  folding,  .but  helps  it 
in  the  second.  , 

A  filter  should  always  be  moistened  with  water  after  it  has  been 
placed  in  the  funnel,  in  order  that  the  fibres  of  the  paper  may  be 
swollen  and  the  size  of  its  pores  diminished,  before  any  of  the  mut- 
ter to  be  filtered  can  pass  into  them. 

Coarse  and  rapid  filtration  —  as  in  the  preparation 
of  reagents  —  can  be  effected  with  paper  filters  of  large 
size,  or  with  cloth  bags ;  also  by  pluggingjhe  neck  of 
a  funnel  or  leg  of  a  siphon  loosely  with  tow  or  cotton. 
If  a  very  acid  or  very  caustic  liquid,  which  would  de- 
stroy paper,  cotton,  tow  or  wool,  is  to  be  filtered,  the 
best  substances  wherewith  to  plug  the  neck  of  the 
funnel  are  asbestos  and  gun-cotton,  neither  of  which 
is  attacked  by  such  corrosive  liquids. 

71.  Filter-Stand.—  Filters  less  than  two  inches  in 
diameter  may  be  placed  directly  in  the  mouth  of  a  test-tube  with- 


Fig.  4. 


Fig.  5. 


out  need  of  even  a  funnel  to  support 
them ;  and  in  general  the  funnel  which, 
holds  a  filter  may  be  thrust  directly 
into  the  mouth  of  a  test-tube  when- 
ever the  quantity  of  liquid  to  be  fil- 
tered is  small,  if  only  an  ample  exit 
be  provided  for  the  air  in  the  tube, 
in  the  manner  shown  with  the  bottle 
of  Fig.  4. 

But  when  the  quantity  of  liquid  to 
be  liltercd  is  comparatively  large,  or 
the  operations  to  which  the  filtrate 
is  to  be  subjected  require  that  it 
should  be  collected  in  a  beaker  or 
porcelain  dish,  the  funnel  should  have 
an  independent  support.  The  iron 

ring  stand,  described  in  §  76  of  this  Appendix,  may  be  used  for  this 
purpose  in  case  of  need;  but  wooden  stands  of  the  form  repre- 
sented in  Fig.  5,  adapted  expressly  for  holding  funnels,  are  very 


xviii  FILTRATION.  §  72 

convenient  and  not  expensive.  The  horizontal  bar  which  holds  the 
funnel  may  be  fixed  at  any  height  on  the  vertical  square  rod  by 
means  of  a  wedge-shaped  key,  whose  form  is  shown  in  the  figure. 
A  fine-grained  wood,  which  does  not  swell  or  shrink  much,  is  desir- 
able for  filter-stands. 

In  general,  care  should  be  taken  that  the  lower  end  of  the  funnel 
touch  the  side  or  edge  of  the  vessel  into  which  the  filtrate  descends, 
in  order  that  the  liquid  may  not  fall  in  drops,  but  run  quietly  with- 
out splashing. 

72,    Rapid  Filtration.  —  Since  in  the  course  of  an  analysis 
much  time  is  consumed  in  the  process  of  filtration,  it  is  desirable 
that  this  operation  should  be  made  as  rapid  as  possible.    A  con- 
siderable advantage  over  the  ordinary  method  may  be  gained  by 
increasing  the  length  of  the  tube  of  the  funnel  by  the  addition  of  a 
piece  of  glass-tubing  a  metre  or  so  in  length  and  bent  as 
Fig.  6.  represented  in  Fig.  6.     When  the  funnel  and  the  tube  are 
filled  with  liquid,  the  difference  of  pressure  on  the  upper 
and  lower  surfaces  is  great  enough  to  cause  a  very  sensible 
increase  in  the  rapidity  of  the  filtration.    A  far  more  effi- 
cient method  of  hastening  the  process  of  filtration   by 
causing  a  difference  in  pressure  on  the 'upper  and  lower 
surfaces  of  the  liquid  to  be  filtered,  may  be  made  available 
wherever  a  constant  supply  of  water  with  a  fall  of  8  or  10 
feet  can  be  obtained.    The  details  of  the  process  and  of  a 
convenient  form  of  the  apparatus  which  may  be  employed, 
will  be  described  presently ;  the  principle  of  the  method 
is  as  follows  :  — 

The  filtrate  instead  of  being  received  in  a  beaker  as  is 
usual,  is  received  in  a  flask  from  which  the  air  is  more  or  less  com- 
pletely exhausted.     This  exhaustion  is  accomplished  by  the  use  of 
a  sort  of  "  water-pump"  which  is   an  adaptation  of  a  very  simple 
Fig  7  principle.   Let  a  b  and  c  d  be  two  tubes,  arranged 

a  as  represented  in  Fig.  7.     If  water  be  allowed 

Jto  flow  in  a  constant  stream  down  the  tube  a  b 
^  and  the  amount  of  water  supplied  be  properly 
regulated,  that  part  of  the  tube  a  b  which  is  be- 
low the  junction  with  c  d  will  be  filled  with  bub- 
bles of  air,  which  is  drawn  in  continuously 
through  c  d  and  dragged  down  by  the  falling  wa- 
ter; if  the  tube  ate  be  connected  with  a  closed  vessel,  the  air  in  the 
vessel  will  be  gradually  exhausted.  The  efficiency  of  such  a  pump 
depends  in  a  measure  upon  the  relative  size  of  the  tubes  and  the 


§  72  FILTRATION.  xix 

amount  of  water  supplied.  Various  forms  of  apparatus  in  which 
advantage  is  taken  of  this  general  principle  might  be  and  have  been 
devised.  As  adapted  for  purposes  of  filtration  the  apparatus  is 
known  as  Bunsen's  "filter-pump";  on  account  of  the  great  advan- 
tage to  be  gained  by  its  use,  the  apparatus,  and  the  method  of  con- 
ducting the  filtration  will  be  given  in  detail.  . 

A  strong  glass  flask  (for  the  purposes  of  qualitative  analysis,  one 
of  from  2  to  4  ounces  capacity  will  answer)  is  furnished  with  a 
doubly- perforated  caoutchouc  stopper :  through  one  of  the  perfora- 
tions is  thrust  the  neck  of  a  glass  funnel  and  through  the  other  a 
piece  of  No.  7  glass  tubing,  bent  at  a  right  angle.  Fig.  8. 
This  tube  serves  to  connect  the  flask  with  the  appa- 
ratus designed  to  effect  the  rarefaction  of  the  air  in 
the  flask.  If  any  considerable  difference  of  pressure 
were  brought  about  between  the  upper  and  lower 
surfaces  of  the  liquid  in  the  funnel,  the  filter  would 
most  likely  break  and  allow  the  precipitate  to  fall 
into  the  flask.  This  danger  is  obviated  as  follows  : 
—  A  funnel  is  chosen  possessing  an  angle  as  near  60°  as  possible, 
the  walls  of  which  must  be  free  from  inequalities  of  every  sort. 
Into  this  glass  funnel  is  fitted  a  second  funnel  or  rather  cone  of  thin 
platinum  foil,  the  sides  of  which  possess  exactly  the  same  inclina- 
tion as  those  of  the  glass  funnel.  This  platinum  cone  is  made  by 
cutting  out  from  a  piece  of  the  thinnest  platinum  foil  that  can  be  ob- 
tained, a  portion  of  a  circle  as  represented  in  Fig.  9,  a.  For  use 
with  a  funnel  two  inches  in  diameter,  this  circle  may  conveniently 
have  a  radius  of  1  inch.  The  foil  is  then  laid  upon  a  piece  of 
hard  wood  and  a  number  of  small  holes  are  punched  out  of  it. 
A  ready  implement  for  this  purpose  may  be  made  by  grind- 
ing oif  squarely  the  point  of  a  common  sewing-needle  and 
fitting  the  needle  to  a  wooden  handle.  When  gently  tapped 
with  a  hammer,  this  punch  forces  out  a  small  round  bit  of 
the  foil  and,  by  subsequently  rubbing  the  foil  on  the  bottom 
of  a  mortar  with  the  pestle,  any  inequalities  of  surface  are 
avoided.  When  the  foil  has  been  annealed  by  being  heated 
to  redness  in  the  lamp  and  allowed  to  cool,  it  is  bent  up 
into  the  shape  of  a  cone  as  represented  in  Fig.  9,  5.  This 
cone  should  have  the  same  angle  of  inclination  as  the  funnel  in 
which  it  is  to  be  used,  and  it  is  desirable  that  the  funnel  should  be  of 
an  angle  of  60° ;  still  if  the  funnel  be  regular  in  shape,  it  can  be  used 
although  it  varies  somewhat  from  this  angle.  The  cone  is  best 
fitted  to  the  funnel  by  the  following  manipulation. 
13 


XX  FILTRATION.  §  72 

A  solid  cone  of  close-grained  hard  wood,  or  better  of  brass  (Fig. 
10,  rt),  which  has  been  turned  to  an  angle  of  GO0,  is  laid  upon  the 
platinum  foil  in  such  a  position  that  the  apex 
Fig.  10.  Of  the  cone  conies  at  the  centre  of  the  circle  of 
which  the  foil  forms  a  part;  the  foil  is  then 
folded  up  and  shaped-  with  the  fingers  so  that 
it  fits  the  cone  closely.  The  two  edges  of  the 
foil  lap,  and  if  they  were  soldered  in  this  posi- 
tion the  cone  would,  of  course,  have  an  angle 
of  60°.  The  platinum  cone  is  now  inserted  in 
the  funnel  to  be  used,  and  opened  out  a  little 
with  the  fingers,  if  necessary,  so  that  it  fits 
the  glass.  The  funnel  should  differ  so  little  from  60°  that  the 
edges  overlap  each  other  only  slightly  more  or  slightly  less  than 
when  the  foil  was  fitted  to  the  wooden  cone.*  By  means  of  a 
sharp  point  make  two  scratches  on  the  platinum  cone,  to  show  where 
the  overlapping  edges  come  when  the  foil  is  in  position,  and  then 
remove  the  cone  from  the  funnel.  Hold  the  platinum  by  means  of 
a  pair  of  pincers  in  the  same  position  that  it  occupied  when  in  the 
funnel,  which  is  easily  done  by  observing  the  scratches  made.  Then 
heat  the  cone  (Fig.  9,  &)  at  the  outer  overlapping  edge,  with  a  blow- 
pipe flame,  put  on  a  small  amount  of  powdered  borax,  heat  again, 
then  put  on  a  bit  of  pure  gold  and  heat  until  the  gold  melts  and 
solders  the  two  edges  together.  The  cone  should  be  held,  the  gold 
put  on,  and  the  blowpipe-flame  directed  in  such  a  manner  that  the 
melted  gold  will  run  down  towards  the  apex  of  the  cone  and  not 
in  the  contrary  direction.  After  dissolving  off  the  adhering  borax 
with  warm  water,  the  cone  is  ready  for  use.  An  ordinary  paper 
filter,  folded  according  to  the  first  method  of  App.,  §  70  is  introduced 
into  this  compound  funnel  in  the  usual  manner;  when  carefully 
moistened  ancl  so  adjusted  that  no  air-bubbles  are  visible  between 
it  and  the  glass,  this  filter,  when  filled  with  a  liquid,  will  support 
the  pressure  even  of  an  extra  atmosphere  without  breaking. 

A  convenient  form  of  the  Bunsen  pump  is  represented  in  Fig.  11. 
The  tubes  (a&,  6c,  hh)  which,  are  represented  in  the  figure  may 
be  very  conveniently  made  of  quarter- inch  lead  pipe  (see  also,  p.  xxii, 
near  bottom)  and  the  bulb-like  enlargement  at  d  may  also  be  made  of 

*  This  wooden  or  brass  cone  is  not  essential;  the  platinum  cone  could  be  shaped 
in  the  funnel  with  proper  care;  it  is,  however,  very  convenient,  especially  in  a  lab- 
oratory where  there  are  a  number  of  students.  In  procuring  such  a  cone,  it  is  well 
to  lay  out  with  a  protractor  on  a  piece  of  thiu  sheet  tin  an  angle  of  60°,  to  cut  this 
out  and  then  to  give  the  pattern  (templet)  to  the  workman  employed. 


§  72 


xxi 


FILTRATION.  §  72 

of  lead  and  soldered  on  to  the  smaller  pipe.  The  water  is  supplied 
in  not  too  large  amountby  the  cock  a,  aud  as  it  passes  along  the  pipe 
a  b  c  and  into  the  waste  c  k,  it  carries  with  it  a  continual  stream  of 
air  bubbles  dragged  through  h  d.  This  tube,  h  d,  communicates  in- 
directly with  the  flask  F  which  is  not  connected  immediately  with 
the  pump ;  the  connection  is  interrupted  by  the  bottle  E,  furnished 
with  a  perforated  stopper  through  which  pass  three  glass  tubes. 
One  of  these  tubes  connects  with  the  flask  F;  one  (by  means  of 
caoutchouc  tubing)  with  the  lead  pipe  h;  one  with  the  manometer 
m.  The  object  of  this  bottle  E  is  to  prevent  the  flow  of  water  into 
the  flask  F,  in  case,  as  sometimes  happens,  the  operator  in  letting 
.  on  too  rapid  a  stream  of  water  causes  it  to  rise  in  the  bulb  d  and 
flow  over  into  the  tube  h  h.  All  the  connectors  should  be  of  very 
thick  caoutchouc  tubing  tightly  fitted  and  then  varnished  with  a 
strong  solution  of  shellac ;  the  stopper  of  the  bottle  E  may  be  treated 
in  the  same  manner. 

The  manometer-bottle  G  is  a  convenient  but  not  absolutely  essen- 
tial addition.  It  consists  simply  of  a  small  bottle  containing  a  quan- 
tity of  mercury,  to  the  surface  of  which  the  atmosphere  has  access 
through  a  small  glass  tube.  The  tube  m  dips  below  the  mercury 
and  connects  with  the  bottle  E.  As  the  air  is  rarified  in  E  (and  in 
the  flask  F},  the  mercury  rises  in  the  tube  m;  this  tube  may  be 
divided  into  centimetres  or  inches  by  means  of  a  file,  or  it  may  be 
provided  with,  or  attached  to,  a  paper  or  wooden  scale. 

The  amount  of  rarefaction  that  can  be  produced  by  this  means 
depends,  of  course,  upon  the  head  of  water  accessible,  and  this  will 
be  determined  by  the  difference  in  height  between  the  points  b  and  k, 
the  extremity  of  the  waste-pipe.  With  a  fall  of  35  ft.  it  is  possible 
to  obtain  nearly  a  perfect  vacuum,  but  a  fall  of  8  or  10  feet  is  suffi- 
cient for  the  purposes  of  qualitative  analysis. 

In  operating  the  filter-pump  certain  precautions  should  be  ob- 
served. Care  should  be  taken  that  the  water  be  not  supplied  in  too 
large  an  amount.  To  this  'end  it  is  well  to  have  the  cock  or  valve 
so  arranged  as  to  make  it  impossible  to  let  on  more  water  than  ex- 
perience shows  to  be  necessary.  The  greatest  effect  is  produced  by 
the  smallest  amount  of  water  that  will  drag  the  air  down  the  pipe 
c  k  in  the  form  of  bubbles,  and  in  order  to  observe  the  flow  of  air  it 
is  well  to  make  a  portion  of  the  pipe  k  of  glass.  (For  that  matter, 
all  the  pipes  may  be  made  of  glass  tubes  joined  by  thick  caoutchouc 
connector;  glass  tubing  of  size  No.  5  (see  App.,  §  82)  will  answer; 
and  the  bulb  d  may  also  be  blown  of  glass  by  a  person  possessing 
sufficient  skill.)  In  using  the  pump  the  water  should  be  let  on  before 


§§73,74         POK  CELAIN  DISHES.  —  LAMPS.  xxiii 

the  connection  is  made  with  the  filtering  flask  and  the  flask  should 
be  removed  before  the  water  is  shut  off. 

73.  Porcelain  Dishes  and  Crucibles.  —  Small  open  dishes 
which  will  bear  heat  without  cracking,  are  much  used  for  boiling 
and  evaporating  liquids.     The  best  evaporating-dishes  are  those 
made  of  Berlin  porcelain,  glazed  both  inside  and  out,  and  provided 
with  a  little  lip  projecting  beyond  the  rim.    The  dishes  made  of 
Meissen  porcelain  are  not  glazed  on  the  outside,  and  are  not  so 
durable  as  those  of  Berlin  manufacture ;  but  they  are  much  cheaper, 
and  with  proper  care  last  a  long  time. 

The  small  Berlin  dishes,  Nos.  "  00,"  "  0,"  and  "  1,"  are  well  suited 
for  all  the  requirements  of  this  work.  They  will  generally  bear  an 
evaporation  to  dryness  and  subsequent  ignition  over  the  open  flame 
of  a  gas  lamp,  —  as  when  ammonium  salts  are  expelled  from  Class 
VII  (§  41),  — but  it  is  well  to  protect  the  dish  somewhat  by  placing 
it  upon  a  piece  of  wire-gauze,  rather  than  to  support  it  upon  a  sim- 
ple triangle.  The  Meissen  dishes  do  not  so  well  endure  an  open 
flame.  The  cheaper  kinds  of  evaporating  dishes,  made  of  "  semi- 
porcelain,"  should  never  be  subjected  to  this  severe  treatment; 
they  are,  for  that  matter,  unfit  for  use  in  qualitative  analysis. 

Very  thin,  highly  glazed  porcelain  crucibles,  with  glazed  covers, 
are  made  both  at  Berlin,  and  at  Meissen  near  Dresden.  In  general 
the  Meissen  crucibles  are  thinner  than  the  Berlin,  but  the  Berlin 
crucibles  are  somewhat  less  liable  to  crack ;  both  kinds  are  glazed 
inside  and  out,  except  on  the  outside  of  the  bottom:  The  Berlin 
Nos.  "  00"  and  "  0,"  respectively  1  1-4  and  1  1-2  inches  in  diameter, 
are  best  suited  for  the  purposes  of  this  manual.  As  the  covers  are 
much  less  liable  to  be  broken  than  the  crucibles,  it  is  advantageous 
to  buy  more  crucibles  than  covers,  whenever  it  is  possible  so  to  do. 
Porcelain  crucibles  are  supported  over  the  lamp  on  an  iron-wire 
triangle ;  they  must  always  be  gradually  heated,  and  never  brought 
suddenly  into  contact  with  any  cold  substance  while  they  are  hot. 

74.  Lamps. —  The  common  spirit-lamp  will  be  understood  with- 
out description  from  the  figure  (Fig.  12).     When  not       Fig,  12. 
actually  lighted,  the  wick  must  be  kept  covered  with 

the  glass  cap ;  for  if  the  wick  were  exposed  to  the 
air,  the  alcohol  in  the  spirit  upon  it  would  evaporate 
faster  than  the  water,  and  the  cotton  would  soon  be- 
come water-soaked  and  incapable  of  being  lighted. 

Whenever  gas  can  be  obtained,  gas-lamps  are 
greatly  to  be  preferred  to  the  best  spirit-lamps.  For 
all  ordinary  uses,  the  gas-lamp  known  as  Bunsen's 


XXIV 


LAMPS. 


§74 


burner  may  be  employed.    The  cheapest  and  best  construction  of 
the  lamp  may  be  learned  from  the  following  description  with  the 


Fig. 13. 


accompanying  figure.  (Fig.  13.)  The 
single  casting  of  brass  a  b  comprises 
the  tube  b  through  which  the  gas  en- 
ters, and  the  block  a  from  which  the 
gas  escapes  by  two  or  three  fine  verti- 
cal holes  passing  through  the  screw  d 
and  issuing  from  the  upper  face  of  d, 
as  shown  at  e.  The  length  of  the  tube 
b  is  4.5  c.  m.,  and  its  outside  diameter 
varies  from  0.5  c.  m.  at  the  outer  end 
to  1  c.  m.  at  the  junction  with  the 
block  a.  The  outside  diameter  of  the 
block  a  is  1.6  c.  m.,  and  its  outside  height  without  the  screws  is  1.8 
c.  m.  By  the  screw  c,  the  piece  a  &  is  attached  to  the  iron  foot  0, 
which  may  be  6  c.  m.  in  diameter.  By  the  screw  d,  the  brass  tube 
/  is  attached  to  the  casting  a  b.  The  diameter  of  the  face  e,  and 
therefore  the  internal  diameter  of  the  tube  /  should  be  8  m.  m. 
The  length  of  the  tube/  is  9  c.  m.  Through  the  wall  of  this  tube, 
four  holes  5  m.  m.  in  diameter,  are  to  be  cut  at  such  a  height  that, 
the  bottom  of  each  hole  will  come  1  m.  m.  above  the  face  e  when 
the  tube  is  screwed  upon  a  b.  These  holes  are  of  course  opposite 
each  other  in  pairs.  The  finished  lamp  is  also  shown  in  the  figure. 
To  the  tube  b  a  caoutchouc  tube  of  5  to  7  m.  m.  internal  diameter  is 
attached ;  this  flexible  tube  should  be  about  1  m.  long,  and  its  other 
extremity  should  be  connected  with  the  gas-cock  through  the  in- 
tervention of  a  short  piece  of  brass  gas-pipe  screwed  into  the  cock. 
In  cases  where  a  very  small  flame  is  required,  as,  for  instance,  in 
evaporating  small  quantities  of  liquid,  a  piece  of  wire  gauze  some- 
what larger  than  the  opening  of  the  tube  /  should  be  laid  across  the 
top  of  the  tube,  and  its  projecting  edges  pressed  down  tightly 
against  the  sides  of  the  tube  before  the  gas  is  lighted.  In  default 
of  this  precaution,  the  flame  of  a  Bunsen 
burner,  when  small  and  exposed  to  currents 
of  air,  is  liable  to  pass  down  the  tube  and 
ignite  the  gas  at  d. 

A  smaller  and  somewhat  cheaper  lamp, 
made  on  the  same  principle  as  the  ordinary 
Bunsen  burner,  is  represented  in  Fig.  14. 
The  "tip"  of  the  burner  is  cast  of  brass, 
and  the  construction  will  be  evident  from 
the  enlarged  section  (b).  The  stand  or  foot 


Pig.14. 


§  75 


BLAST-LAMPS. 


XXV 


Fig.  15. 


is  the  same  as  shown  ID  Fig.  13,  except  that  the  opening  for  the 
gas  is  larger.  These  lamps  are  excellent  where  a  small  flame  is  re- 
quired, as  it  is  almost  impossible  for  the  gas  to  "back  down"  and 
ignite  at  the  lower  opening.  Tips  are  also  made,  as  shown  at  c  : 
here  the  upper  opening  is  closed,  and  the  gas  issues  from  smaller 
openings  in  the  sides  of  the  tube  forming  a  "  rose  ";  this  form  of 
burner  is  of  especial  service  when  evaporating  a  solution  in  a  porce- 
lain dish  where  it  is  desirable  to  heat  the  liquid  equably.  Either  of 
the  tips  described  may  be  screwed  upon  an  ordinary  gas-burner  in 
default  of  the  stand  or  foot  above  represented.  These  burners  can 
be  procured  of  M.  W.  Pierce  &  Co.,  Gas  and  Steam  Fitters,  Boston, 
Mass. 

75.  Blast-lamps  and  Blowers.  —  Though  well  suited  for  all 
the  ordinary  operations  of  the  labor- 
atory, the  lamps  above  described  are 
incapable  of  yielding  a  very  intense 
heat.  Hence,  when  the  contents  of 
a  platinum  crucible  are  to  be  fused 
or  intensely  heated,  a  blast-lamp 
will  be  found  useful.  The  best  form 
is  that  sold  under  the  name  of  Bun- 
sen's  Gas  Blowpipe.  Its  construc- 
tion and  the  method  of  using  it  may 
be  learned  from  the  accompanying 
figure ;  a  b  is  the  pipe  through  which 
the  gas  enters,  c  is  the  tube  for  the 
blast  of  air ;  the  relation  of  the  air- 
tube  to  the  external  gas  tube  is 
shown  at  d;  there  is  an  outer  slid- 
ing tube  by  which  the  form  and 
volume  of  the  flame  can  be  regu- 
lated. 

If  gas  is  not  to  be  had,  a  lamp  burning  oil  or  naphtha  may  be  em- 
ployed. Figure  16  represents  a  glass- 
blower's  lamp,  made  of  tin  and  suita- 
ble for  burning  oil.  A  large  wick  is 
essential,  whether  oil  or  naphtha  be 
the  combustible. 

For  every  blast-lamp  a   blowing- 
machine  of  some  sort  is  necessary. 

To  supply  a  constant  blast  it  is  essential  that  the  bellows  be 
of  that  construction  called  double. 


Pig.  16. 


XXVI 


BLOWERS. 


§75 


Fig.  17  represents  a  very  good  form  of  blowpipe- table,  made  by 
J.  H.  Call,  North  Billerica,  Mass.,  and  costing  about  thirty  dollars. 
The  bellows  are  made  of  seamless  rubber  cloth ;  the  table  is  0.8  metre 

Fig.  17. 


high,  from  which  the  other  dimensions  may  be  inferred.  A  simpler 
form  of  bellows,  and  one  which  can  be  made  by  any  carpenter  or 
cabinet-maker,  is  represented  in  perspective  and  in  section  in 

Fig.  18. 


Fig.  18.  The  sides  of  the  bellows  and  of  the  reservoir  are  made 
of  stout  leather.  The  arrangement  of  valves  will  be  evident  from 
the  figure ;  a  constant  pressure  is  maintained  on  the  reservoir  by 
means  of  a  spiral  spring,  and  the  air  is  delivered  through  the  tube  t. 
The  rod  which  is  represented  in  the  figure  serves  simply  as  a 
guide.  The  entire  length  from  a  to  &  may  be  O.G  metre. 


§75 


BLOWERS. 


XXVll 


Where  an  abundant  supply  of  water  is  at  command,  a  Bunsen 
pump  of  the  kind  described  in  App.,  §  72,  but  of  larger  size,  may  be 
used  to  furnish  a  blast.  The  pipe  above  the  enlargment  d  (see  Fig. 


Fig.  19. 


11)  is  left  open  to  the  air  instead  of  connecting 
with  a  flask  as  represented  in  Fig.  11.  The 
waste-pipe  k  passes  through  the  cork  of  large 
bottle,  Fig.  19,  of  some  litres  capacity.  Through 
the  stopper  of  this  bottle  there  pass  also  two 
glass  tubes ;  one  of  them,  ft,  reaches  nearly  to  the 
bottom  of  the  bottle  and  serves  as  a  siphon ;  the 
other  merely  extends  through  the  cork,  and  to 
it  is  attached  the  tube  i,  to  convey  the  blast  to 
any  desired  point.  The  water  and  air  which 
together  flow  down  the  pipe  k  &,  pass  into  the 
bottle.  When  the  water  is  turned  on,  the 
caoutchouc  tube  g  i  is  closed  for  a  moment  with 
the  thumb  and  finger.  This  starts  the  water 
through  the  siphon,  and  immediately  a  con- 
tinuous and  powerful  blast  of  air  rushes  out 
through  the  tube  g  i,  and  may  be  carried  directly 
to  the  blow-pipe.  The  siphon  must  be  capable 
of  carrying  off  a  larger  stream  of-  water  than  that  which  is  allowed 
to  enter,  so  that  there  shall  never  be  more  than  3  or  4  c.  m.  of  water 
in  the  bottle. 

The  efficiency  of  the  blast  depends  upon  the  dimensions  of  the 
tubes  and  the  head  of  water  employed ;  one  of  the  Bunsen  pumps 
in  the  laboratory  of  the  Institute  of  Technology  used  to  furnish  a 
blast  for  the  blowpipe  is  made  of  half-inch  lead  pipe  and  there  is  a 
fall  of  about  30  feet.  It  is,  however,  by  no  means  necessary  to  have 
so  great  a  fall ;  a  fall  of  6  or  8  feet  furnishes  an  efficient  blast,  but 
the  amount  of  water  used  is  much  larger. 

In  default  of  a  blast  lamp,  platinum  crucibles  may  readily  be 
ignited  in  a  fire  of  coke  or  anthracite.  To  this  end,  place  the  tightly 
covered  platinum  crucible  in  a  somewhat  larger  crucible  of  refractory 
clay  or  Hessian  ware,  and  pack  the  space  between  the  two  cruci- 
bles tightly  with  calcined  magnesia,  so  that  the  platinum  may  no- 
where come  in  contact  with  the  clay.  Cover  the  coarse  crucifele, 
and  place  it,  with  its  contents,  in  the  coal  fire,  in  such  a  manner  that 
it  may  be  gradually  heated ;  finally,  imbed  the  crucible  in  the  glow- 
ing coals  and  urge  the  draught  of  the  furnace  for  half  an  hour. 
The  degree  of  heat  to  which  the  contents  of  the  platinum  crucible 
may  be  exposed,  in  this  way,  in  an  efficient  fire,  is  really  far  greater 


XXV111 


LAMPS. 


§  76 


Fig.  20. 


than  that  of  the  blast  lamps  above  described ;  but  the  lamps  are 
more  convenient  than  the  fire. 

The  effect  of  a  simple  Bunsen's  burner  may  be  greatly  increased, 
without  the  use  of  any  blower,  by  surrounding  its  flame  with  a 
cylinder  of  fire  clay,  3  inches  in  diameter  by  4  or  5  inches  high,  and 
having  walls  at  least  3-8  of  an  inch  thick.  The  crucible,  or  other 
body  to  be  heated,  is  hung  in  the  middle  of  this  chimney,  and  is 
thus  exposed  not  only  to  the  direct  heat  of  the  flame,  but  also  to  the 
radiant  heat  from  the  clay  walls  which  surround  it. 

Where  no  gas  is  to  be  had,  an  alcohol  lamp  with  circular  wick,  of 
some  one  of  the  numerous  forms  sold  under  the  name  of  Berzelius's 

Argand  Spirit  Lamp  (Fig.  20), 
will  be  found  useful.  These 
argand  lamps  are  usually 
mounted  on  a  lamp-stand  pro- 
vided with  three  brass  rings ; 
but  the  fittings  of  these  lamps 
are  all  made  slender,  in  order 
not  to  carry  off  too  much 
heat.  When  it  is  necessary 
to  heat  heavy  vessels,  other 
supports  must  be  used. 

76.  Iron-stand,  Tripod, 
Wire-gauze  and  Triangle. 
—  To'  support  vessels  over  the 
gas-lamp,  an  iron  stand  is  used 
consisting  of  a  stout  vertical 
rod  fastened  into  a  heavy, 

cast-iron  foot,  and  several  iron  rings  of  graduated  sizes  secured  to 
the  vertical  rod  with  binding  screws ;  all  the  rings  may  be  slipped 

Fig  21  off  the  rod'  or  any  rin£  mav  be  adjusted  at  any  coa~ 
venient  elevation.  The  general  arrangement  is  not 
unlike  that  of  the  stand  which  makes  part  of  the  Ber- 
zelius  lamp  (Fig.  20),  although  simpler  and  cheaper. 
As  a  general  rule,  it  is  not  best  to  apply  the  direct 
flame  to  glass  and  procelain  vessels ;  hence  a  piece  of 
iron  wire-gauze  of  medium  fineness  is  stretched  loosply 
over  the  largest  ring,  and  bent  downwards  a  little  for 
the  reception  of  round-bottomed  vessels ;  on  this 
gauze,  flasks  and  porcelain  dishes  are  usually  sup- 
ported. Crucibles,  or  dishes,  too  small  for  the  small- 
est ring  belonging  to  the  stand,  are  conveniently  sup- 
ported  on  an  equilateral  triangle  made  of  three  pieces 


§77 


WATER-  AND  SAND-BATH. 


XXIX 


Fig.  22. 


Fig.  23. 


of  soft  iron  wire  twisted  together  at  the  apices  ;  this  triangle  is  laid 

on  one  of  the  rings  of  the  stand.   An  iron  tripod,  — 

that  is,  a  stout  ring  supported  on  three  legs,  — 

may  often  be  used  instead  of  the  stand  above 

described,  but  it  is  not  so  generally  useful  be- 

cause of  the  difficulty  of  adjusting  it  at  vari- 

ous   heights;     with    a    sufficiency    of    wooden 

blocks  wherewith  to  raise  the  lamp  or  the  tripod 

as  occasion  may  require,  it  may  be  made  availa- 

ble. 

77,  Water-bath  and  Sand-bath.  —  It  is  often  necessary  to 
evaporate  solutions,  or  to  dry  precipitates  at  a  moderate  tempera- 
ture which  can  permanently  be  kept  below  a  certain  known  limit; 
thus,  when  an  aqueous  solution  is  to  be  quietly  evaporated  without 
spirting  or  jumping,  the  temperature  of  the  solution  must  never  be 
suffered  to  rise  above  the  boiling-point  of  water,  nor  even  quite  to 
reach  this  point.  This  quiet  evaporation  is  best 
effected  by  the  use  of  a  water-bath,  —  a  copper 
cup  whose  top  is  made  of  concentric  rings  of  dif- 
ferent diameters  to  adapt  it  to  dishes  of  various 
sizes  (Fig.  23).  This  cup,  two  thirds  full  of  water* 
is  supported  on  the  iron-stand  over  the  lamp,  and 
the  dish  containing  the  solution  to  be  evaporated 
is  placed  on  that  one  of  the  several  rings  which 
will  permit  the  greater  part  of  the  dish  to  sink 
into  the  copper  cup.  The  steam  rising  from  the 
water  impinges  upon  the  bottom  of  the  dish,  and  brings  'the  liquid 
within  it  to  a  temperature  which  insures  the  evaporation  of  the 
water,  but  will  not  cause  any  actual  ebullition.  The  water  in  the 
copper  cup  must  never  be  allowed  to  boil  away.  Wherever  a  con- 
stant supply  of  steam  is  at  hand,  as  in  buildings  warmed  by  steam, 
the  copper  cup  above  described  may  be  converted  into  a  steam-bath 
by  attaching  it  to  a  steam-pipe  by  means  of  a  small  tube  provided 
with  a  stop-cock. 

An  empty  tomato-can  furnished  with  rings  as  above  may  take  the 
place  of  the  copper  cup,  and,  in  fact,  a  cheap  but  serviceable  water- 
baih  may  be  made  from  a  quart  milk-can,  oil-can,  tea-canister,  or 
any  similarly  shaped  tin  vessel,  by  inserting  the  stem  of  a  glass  funnel 
into  the  neck  of  the  can  through  a  well-  fitting  cork.  In  this  funnel  the 
dish  containing  the  liquor  to  be  evaporated  rests.  The  can  contains 
the  water,  which  is  to  be  kept  just  boiling.  On  account  of  the  shape 


XXX 


BLOWPIPES. 


§  78 


Fig.  24. 


of  the  funnel,  dishes  of  various  sizes  can  be  used  with  the  same 
apparatus. 

When  a  gradual  and  equable  heat  higher  than  can  be  obtained 
upon  the  water-bath  is  required,  a  sand-bath  will  sometimes  be 
found  useful.  A  cheap  and  convenient  sand-bath  may  be  made  by 
beating  a  disk  of  thin  sheet  iron,  about  four  inches  in  diameter,  into 
the  form  of  a  saucer  or  shallow  pan,  and  placing  within  it  a  small 
quantity  of  dry  sand.  The  dish  or  flask  to  be  heated  is  imbedded  in 
the  sand,  and  the  apparatus  placed  upon  a  ring  of  the  iron-stand 
over  a  gas-lamp. 

73.  Blowpipes.  —  The  mouth-blowpipe  in  its  simplest  form  is 
a  tube  bent  near  one  extremity  at  a  right  angle.  Fig.  24,  a,  repre- 
sents a  common  form  of  blowpipe  used  by  jewellers.  The  blowpipe 
is  rendered  more  convenient  by  the  addition  of  a  mouth-piece  and  a 
chamber  near  the  right  angle  for  the  condensa- 
tion of  moisture.  Fig.  24,  6  and  c,  represent 
different  forms  of  blowpipe  thus  furnished. 
The  cheapest  and  best  form  of  mouth  blowpipe 
for  chemical  purposes  is  a  tube  of  tin-plate, 
about  18  c.  m.  long,  2  c.  m.  broad  at  one  end, 
and  tapering  to  0.7  c.  m.  at  the  other  (Fig.  24, 
6)  ;  the  broad  end  is  closed,  and  serves  to  re- 
tain the  moisture ;  a  little  above  this  closed 
end  a  small  cylindrical  tube  of  brass  about 
5  c.  m.  long  is  soldered  in  at  right  angles ;  this 
brass  tube  is  slightly  conical  at  the  end,  and  car- 
ries a  small  nozzle  or  tip,  which  may  be  made 
either  of  brass  or  platinum.  The  tip  should  be 
drilled  out  of  a  solid  piece  of  metal,  and  should 
not  be  fastened  upon  the  brass  tube  with  a 
screw.  A  trumpet-shaped  mouth-piece  of  horn  or  boxwood  is  a  con- 
venient, though  by  no  means  essential,  addition  to  this  blowpipe. 
For  convenience  in  cleaning  and  packing,  blowpipes  are  often  made 
in  several  pieces,  as  is  the  one  represented  in  Fig  24,  c. 

The  blowpipe  may  be  used  with  a  candle,  with  gas  or  with  any 
hand-lamp  proper  for  burning  oil,  petroleum  or  any  of  the  so-called 
burning  fluids,  provided  that  the  form  of  the  lamp  below  the  wick- 
holder  is  such  as  to  permit  the  close  approach  of  the  object  to  be 
heated  to  the  side  of  the  wick.  When  a  lamp  is  used,  a  wick  about 
1.2  c.  m.  long  and  6.5  c.  m.  broad  is  more  convenient  than  a  round 
or  narrow  wick.  The  wick-holder  should  be  filed  off  on  its  longer 
dimension  a  little  obliquely,  and  the  wick  cut  parallel  to  the  holder, 


§  78 


BL  0  WPIPE-FLAME. 


XXXI 


in  order  that  the  blowpipe  flame  may  be  directed  downwards  when 
necessary  (Figs.  25  and  26).  A  gas  flame  suitable  for  the  blowpipe 
is  readily  obtained  by  slipping  a  narrow  brass  tube  (f),  open  at  both 
ends,  into  the  tube  /  of  Bunsen's  burner.  (See  Fig.  13.)  This 
blowpipe-tube  must  be  long  enough  to  close  the  air  apertures  in  the 
tube  /,  and  should  be  pinched  together  and  filed  off  obliquely  on  top ; 
it  may  usually  be  obtained  with  the  burner  from  dealers  in  chemical 
ware. 

To  use  the  mouth  blowpipe,  place  the  open  end  of  the  tube  be- 
tween the  lips,  or,  if  the  pipe  is  provided  with  a  mouth-piece,  press 
the  trumpet-shaped  mouth-piece  against  the  lips;  fill  the  mouth 
with  air  till  the  cheeks  are  widely  distended,  and  insert  the  tip  in 
the  flame  of  a  lamp  or  candle ;  close  the  communication  between  the 
lungs  and  the  mouth,  and  force  a  current  of  air  through  the  tube 
by. squeezing  the  air  in  the  mouth  with  the  muscles  of  the  cheeks, 
breathing,  in  the  meantime,  regularly  and  quietly  through  the  nos- 
trils. The  knack  of  blowing  a  steady  stream  for  several  minutes  at 
a  time,  is  readily  acquired  by  a  little  practice.  It  will  be  at  once  ob- 
served that  the  appearance  of  the  flame  varies  considerably,  accord- 
ing to  the  strength  of  the  blast  and  the  position  of  the  jet  with 
reference  to  the  wick. 

When  the  jet  of  the  blowpipe  is  inserted  into  the  middle  of  a 
candle-flame,  or  is  placed  in  pig<  25. 

the  lamp-flame  in  the  posi- 
tion shown  in  Fig.  25,  and  a 
strong  blast  is  forced  through 
the  tube,  a  long,  blue  cone  of 
flame,  a  6,  is  produced,  be- 
yond and  outside  of  which 
stretches  a  more  or  less  col- 
ored outer  cone  towards  c. 
The  point  of  greatest  heat  in  this  flame  is  at  the  point  of  the  inner  blue 
cone,  because  the  combustible  gases  are  there  supplied  with  just  the 
quantity  of  oxygen  necessary  to  consume  them,  but  between  this  point 
and  the  extremity  of  the  flame  the  combustion  is  concentrated  and  in- 
tense. The  greater  part  of  the  flame  thus  produced  is  oxidizing  in  its 
effect,  and  this  flame  is  technically  called  the  oxidizing  flame.  From  the 
point  a  of  the  inner  blue  cone,  the  heat  of  the  flame  diminishes  in  both 
directions,  towards  b,  on  the  one  hand,  and  towards  c  on  the  other ; 
most  substances  require  the  temperature  which  is  found  between  a 
and  c.  Oxidation  takes  place  most  rapidly  at,  or  just  beyond  the 
point  c  of  the  flame,  provided  that  the  temperature  at  this  point  is 
high  enough  for  the  special  substance  to  be  heated. 
14 


XXX11 


BL  0  WPIPE-FLANE. 


§§  78,79 


Fig.  27. 


A  flame  of  precisely  the  opposite  chemical  effect  may  be  produced 
with  the  blowpipe.  To  obtain  a  good  reducing  flame,  it  is  necessary 
to  place  the  tip  of  the  blowpipe,  not  within,  but  just  outside  of  the 

flame,   and  to  blow  rather 

Fig.  26.  over  than  through  the  mid- 

die  of  the  flame  (Fig.  26). 
In  this  manner,  the  flame  is 
less  altered  in  its  general 
character  than  in  the  former 
case,  the  chief  part  consist- 
ing of  a  large,  luminous  cone, 
containing  a  quantity  of  free 
carbon  in  a  state  of  intense 
ignition,  and  just  in  the  condition  for  taking  up  oxygen.  This  flame 
is,  therefore,  reducing  in  its  effect,  and  is  technically  called  the  re- 
ducing  flame.  The  substance  which  is  to  be  reduced  by  exposure 
to  this  flame,  should  be  completely  cov- 
ered up  by  the  luminous  cone,  so  that 
contact  with  the  air  may  be  entirely 
avoided.  It  is  to  be  observed  that, 
whereas  to  produce  an  effective  oxidiz- 
ing flame  a  strong  blast  of  air  is  desira- 
ble, to  get  a  good  reducing  flame,  the 
operator  should  blow  gently,  with  only 
enough  force  to  divert  the  lamp-flame. 

Substances  to  be  heated  in  the  blow- 
pipe flame,  are  supported,  sometimes  on 
charcoal,  and  sometimes  on  platinum  foil 
or  wire,  or  in  platinum  spoons  or  forceps. 

Charcoal  is  especially  suitable  for  a  support  in  experiments  of  re- 
duction. With  reference  to  the  choice  of  charcoal  for  blowpipe 
experiments,  see  §  81.  The  manner  of  holding  the  blowpipe  is 
illustrated  by  Fig.  27. 

79.  Platinum  Foil  and  Wire.  —  Pincers.  —  A  piece  of  plati- 
num foil  about  1  1-2  inches  long,  and  1  inch  wide  will  be  sufficient. 
The  foil  should  be  at  least  so  thick  that  it  does  not  crinkle  when 
wiped ;  and  it  is  more  economical,  to  get  foil  which  is  too  thick  than 
too  thin,  for  it  requires  frequent  cleaning.  To  keep  foil  in  good 
order  it  should  be  frequently  scoured  with  fine  moist  sand,  and  in 
case  the  foil  becomes  wrinkled  it  may  be  burnished  by  placing  it 
upon  the  bottom  of  an  inverted  agate  or  porcelain  mortar  and  rub- 
bing it  strongly  with  the  pestle. 


§  80,  81  PLATINUM  UTENSILS.  XXxiii 

A  bit  of  platinum  wire,  not  stouter  than  the  wire  of  a 
small  pin  and  about  3  inches  long,  will  last  a  long  time     •Fig*  28% 
with  careful  usage.    It  may  be  cleaned  by  long-continued         /~\ 
boiling  in  water.    A  small  loop  about  as  large  as  this  O, 
should  be  bent  at  each  end  of  the  wire. 

When  platinum  foil  is  to  be  heated,  it  may  be  held  at 
one  end  with  a  pair  of  the  small  steel  pincers  known  as 
jewellers'  tweezers.  A  piece  of  platinum  wire,  as  long 
as  the  one  above  described,  can  be  held  in  the  fingers 
without  inconvenience,  for  platinum  is,  comparatively 
speaking,  a  bad  conductor  of  heat.  Pieces  of  wire,  too 
short  to  be  held,  may  be  made  serviceable  by  thrusting 
one  end  of  the  wire  into  the  end  of  a  glass  rod  or  closed 
tube  which  has  been  softened  in  the  blowpipe  flame. 

80.  Platinum   Crucibles. —For  several  of  the        \ 
operations  of  quantitative  analysis  as  now  practised, 
platinum  crucibles  are  indispensable,  and  though  not        O 
absolutely  necessary  for  the  profitable  study  of  qualita- 
tive analysis,  one  of  these  vessels  will  often  be  found  conven- 
ient by  the  student  of  the  elements  of  analysis.     It  will  be  well, 
therefore,  for  the  student,  who  proposes  to  continue   his  chemi- 
cal studies   beyond  qualitative   analysis,   to  procure  a  platinum 
crucible  once  for  all.     A  crucible  of  the  capacity  of  about  20  cubic 
centimetres  will  be  large  enough  for  most  uses ;  it  should  be  cylin- 
drical rather  than  flaring,  and  should  be  provided  with  a  loose 
cover  in  the  form  of  a  shallow  dish.  For  the  purposes  of  this  book, 
however,  a  small  crucible  holding  7  or  8  cubic  centimetres  answers 
every  purpose  and  a  cover  is  not  essential. 

No  other  metal,  and  no  mixture  of  substances  from  which  a  metal 
can  be  reduced,  must  ever  be  heated  in  a  platinum  crucible,  or  upon 
platinum  foil  or  wire,  for  platinum  forms  alloys  with  other  metals, 
and  these  alloys  are  much  more  fusible  than  platinum  itself.  If 
once  alloyed  with  a  baser  metal,  the  platinum  ceases  to  be  applica- 
ble to  its  peculiar  uses. 

Platinum  may  be  cleaned  by  boiling  it  in  either  nitric  or  chlorhy- 
dric  acid,  by  fusing  acid  sulphate  of  sodium  upon  it,  or  by  scouring 
it  with  fine  sand.  Aqua  regia  aud  chlorine-water  dissolve  platinum ; 
the  sulphides,  cyanides,  and  hydrates  of  sodium  and  potassium, 
when  fused  in  platinum  vessels,  slowly  attack  the  metal. 

81.  Wash-bottle.  —  A  wash-bottle  is  a  flask  with  a  uniformly 
thin  bottom  closed  with  a  sound  cork  or  caoutchouc  stopper  through 
which  pass  two  glass  tubes,  as  shovvn  in  Fig.  29. 


xxxiv  GLASS—  TUBING.  STIBKING-BODS.      §  82,  83 


Fig.  29. 


The  outer  end  of  the  longer  tube  is  drawn  to  a 
moderately  fine  point.  A  short  bend  near  the  bottom 
of  this  longer  tube  in  the  same  plane  and  direction  as 
the  upper  bend  is  of  some  use,  because  it  enables  the 
operator  to  empty  the  flask  more  completely  by  in- 
clining it.  By  blowing  into  the  short-tube,  a  stream 
of  water  will  be  driven  out  of  the  long  tube  with  con- 
siderable force.  This  force  with  which  the  stream  is 
projected  adapts  the  apparatus  to  removing  precipi- 
tates from  the  sides  of  vessels  as  well  as  to  washing 
them  on  filters.  For  use  in  analytical  operations,  it 
is  often  convenient  to  attach  a  caoutchouc  tube  12  or 
15  c.  m.  long  to  the  tube  through  which  the  air  is 
blown ;  this  flexible  tube  should  be  provided  with  a 
glass  mouth-piece,  consisting  of  a  bit  of  glass  tubing  about  3  c.  m. 
long.  As  the  wash-bottle  is  often  filled  with  hot  or  even  boiling 
water,  it  may  be  improved  by  binding  about  its  neck  a  ring  of  cork, 
or  winding  the  neck  closely  with  smooth  cord.  It  may  then  be 
handled  without  inconvenience,  when  hot. 

The  method  of  making  awash-bottle  is  described  in  the  following 
paragraphs. 

82.  Glass  Tubing.  —  Two  qualities  of  glass  tubing  are  used  in 
chemical  experiments,  that  which  softens  readily  in  the  flame  of  a 
gas-  or  spirit-lamp,  and  that  which  fuses  with  extreme  difficulty  in 
the  flame  of  the  blast-lamp.  These  two  qualities  are  distinguished 
by  the  terms  soft  and  hard  glass.  Soft  glass  is  to  be  preferred  for 
all  uses  except  the  intense  heating,  or  ignition,  of  dry  substances. 
Tig.  30  represents  the  common  sizes  of  glass  tubing,  both  hard  and 

Fig.  30. 


8      7 


soft,  and  shows  also  the  proper  thickness  of  the  glass  walls  for  each 
size.  The  numbers  ranging  from  4  to  8  are  best  suited  for  use  in 
qualitative  analysis. 

83.  Stirring-rods.  —  Cut  a  short  stick  of  glass  rod,  No.  8  or  7, 
into  pieces  four  or  five  inches  long  (see  the  next  paragraph),  and 
round  the  sharp  ends  by  fusion  in  the  blowpipe  flame. 


§  84      CUTTING  AND  C BACKING  GLASS.      XXXV 

84.  Cutting  and  Cracking  Glass.  —  Glass  tubing  and  glass 
rod  must  generally  be  cut  to  the  length  required  for  any  particular 
apparatus.  A  sharp  triangular  file  is  used  for  this  purpose.  The 
stick  of  tubing,  or  rod,  to  be  cut  is  laid  upon  a  table,  and  a  deep 
scratch  is  made  with  the  file  at  the  place  where  the  fracture  is  to  be 
made.  The  stick  is  then  grasped  with  the  two  hands,  one  on  each 
side  of  the  mark,  while  the  thumbs  are  brought  together  just  at  the 
scratch.  By  pushing  with  the  thumbs  and  pulling  in  the  opposite 
direction  with  the  fingers,  the  stick  is  broken  squarely  at  the  scratch, 
just  as  a  stick  of  candy  or  dry  twig  may  be  broken.  The  sharp 
edges  of  the  fracture  should  invariably  be  made  smooth,  either  with 
a  wet  file,  or  by  softening  the  end  of  the  tube  or  rod  in  the  lamp. 
(App.,  §  85.)  Tubes  or  rods  of  sizes  four  to  eight  inclusive  may 
readily  be  cut  in  this  manner ;  the  larger  sizes  are 
divided  with  more  difficulty,  and  it  is  often  neces- 
sary  to  make  the  file-mark  both  long  and  deep. 
An  even  fracture  is  not  always  to  be  obtained  with 
large  tubes.  The  lower  ends  of  glass  funnels,  and 
those  ends  of  gas  delivery-tubes  which  enter  the 
bottle  or  flask  in  which  the  gas  is  generated,  should 
be  filed  off,  or  ground  off  on  a  grindstone,  obliquely 
(Fig.  31),  to  facilitate  the  dropping  of  liquids  from  such  extremities. 

In  order  to  cut  glass  plates,  the  glazier's  diamond  must  be  resorted 
to.  For  the  cutting  of  exceedingly  thin  glass  tubes  and  of  other 
glass  ware,  like  flasks,  retorts  and  bottles,  still  other  means  are  re- 
sorted to,  based  upon  the  sudden  and  unequal  application  of  heat. 
The  process  divides  itself  into  two  parts,  the  producing  of  a  crack 
in  the  required  place,  and  the  subsequent  guiding  of  this  crack  in 
the  desired  direction.  To  produce  a  crack,  a  scratch  must  be  made 
with  the  file,  and  to  this  scratch  a  pointed  bit  of  red-hot  charcoal, 
or  the  jet  of  flame  produced  by  the  mouth  blowpipe,  or  a  very  fine 
gas-flame,  or  a  red-hot  glass-rod  may  be  applied.  If  the  heat  does 
not  produce  a  crack,  a  wet  stick  or  file  may  be  touched  upon  the  hot 
spot.  Upon  any  part  of  a  glass  surface  except  the  edge,  it  is  not 
possible  to  control  perfectly  the  direction  and  extent  of  this  first 
crack ;  at  an  edge  a  small  crack  may  be  started  with  tolerable  cer- 
tainty by  carrying  the  file-mark  entirely  over  the  edge.  To  guide 
the  crack  thus  started,  a  pointed  bit  of  charcoal  or  slow-match  may 
be  used.  The  hot  point  must  be  kept  on  the  glass  from  1  c.  m.  to 
0.5  c.  m.  in  advance  of  the  point  of  the  crack.  The  crack  will  fol- 
low the  hot  point,  and  may  therefore  be  carried  in  any  desired  di- 
rection. By  turning  and  blowing  upon  the  coal  or  slow-match,  the 


XXXVi  MANIPULATION  OF  GLASS.  §  85 

point  may  be  kept  sufficiently  hot.  Whenever  the  place  of  experi- 
ment is  supplied  with"  common  illuminating  gas,  a  very  small  jet  of 
burning  gas  may  be  advantageously  substituted  for  the  hot  coal  or 
slow  match.  To  obtain  such  a  sharp  jet,  a  piece  of  hard  glass  tube, 
No.  4,  10  c.  m.  long,  and  drawn  to  a  very  fine  point  (App.,  §  85), 
should  be  placed  in  the  caoutchouc  tube  which  ordinarly  delivers  the 
gas  to  the  gas-lamp,  and  the  gas  should  be  lighted  at  the  fine  ex- 
tremity. The  burning  jet  should  have  a  fine  point,  and  should  not 
exceed  1.5  c.  m.  in  length.  By  a  judicious  use  of  these  simple  tools, 
broken  tubes,  beakers,  flasks,  retorts  and  bottles  may  often  be  made 
to  yield  very  useful  articles  of  apparatus.  No  sharp  edges  should 
be  allowed  to  remain  upon  glass  apparatus.  The  durability  of  the 
apparatus  itself,  and  of  the  corks  and  caoutchouc  stoppers  and 
tubing  used  with  it,  will  be  much  greater,  if  all  sharp  edges  are 
removed  with  the  file,  or,  still  better,  rounded  in  the  lamp. 

85.  Bending  and  Closing  Glass  Tubes.  —  Tubing  of  sizes 
four  to  eight  inclusive  can  generally  be  worked  in  the  common  gas- 
or  spirit  lamp ;  for  larger  tubes  the  blast-lamp  is  necessary.  (App., 
§  75.)  Glass  tubing  must  not  be  introduced  suddenly  into  the  hot- 
test part  of  the  flame,  lest  it  crack.  Neither  should  a  hot  tube  be 
taken  from  the  flame  and  laid  at  once  upon  a  cold  surface.  Gradual 
heating  and  gradual  cooling  are  alike  necessary,  and  are  the  more 
essential  the  thicker  the  glass ;  very  thin  glass  will  sometimes  bear 
the  most  sudden  changes  of  temperature,  but  thick  glass  and  glass 
of  uneven  thickness  absolutely  require  slow  heating  and  annealing. 
When  the  end  of  a  tube  is  to  be  heated,  as  in  rounding  sharp  edges, 
more  care  is  required  in  consequence  of  the  great  facility  with  which 
cracks  start  at  an  edge.  A  tube  should,  therefore,  always  be 
brought  first  into  the  current  of  hot  air  beyond  the  actual  flame  of 
the  gas-  or  spirit-lamp,  and  there  thoroughly  warmed,  before  it  is 
introduced  into  the  flame  itself.  If  a  blast-lamp  is  employed,  the 
tube  may  be  warmed  in  the  smoky  flame,  before  the  blast  is  turned 
on,  and  may  subsequently  be  annealed  in  the  same  manner;  the  de- 
posited soot  will  be  burnt  off  in  the  first  instance,  and  in  the  last 
may  be  wiped  off  when  the  tube  is  cold.  In  heating  a  tube,  whether 
for  bending,  drawing,  or  closing,  the  tube  must  be  constantly  turned 
between  the  fingers,  and  also  moved  a  little  to  the  right  and  left,  in 
order  that  it  may  be  uniformly  heated  all  round,  and  that  the  tem- 
perature of  the  neighboring  parts  maybe  duly  raised.  If  a  tube,  or 
rod,  is  to  be  heated  at  any  part  but  an  end,  it  should  be  held  between 
the  thumb  and  first  two  fingers  of  each  hand  in  such  a  manner  that 
the  hands  shall  be  below  the  tube  or  rod,  with  the  palms  upward, 


§  85  MANIPULATION  OF  GLASS.  xxxvii 

While  the  lamp-flame  is  between  the  hands.  When  the  end  of  a  tube 
or  rod  is  to  be  heated,  it  is  best  to  begin  by  warming  the  tube  or 
rod  about  2  c.  m.  from  the  end,  and  thence  to  proceed  slowly  to  the 
end. 

The  best  glass  will  not  be  blackened  or  discolored  during  heating. 
Blackening  occurs  in  glass  which,  like  ordinary  flint  glass,  contains 
lead  as  an  ingredient.  Glass  containing  much  lead  is  not  well 
adapted  for  chemical  uses.  The  blackening  may  sometimes  be  re- 
moved by  putting  the  glass  in  the  upper  or  outer  part  of  the  flame, 
where  the  reducing  gases  are  consumed,  and  the  air  has  the  best 
access  to  the  glass.  The  blackening  may  be  altogether  avoided  by 
always  keeping  the  glass  in  the  oxidizing  part  of  the  flame. 

Glass  begins  to  soften  and  bend  below  a  visible  red  heat.  The 
condition  of  the  glass  is  judged  of  as  much  by  the  fingers  as  the 
eye ;  the  hands  feel  the  yielding  of  the  glass,  either  to  bending, 
pushing,  or  pulling,  better  than  the  eye  can  see  the  change  of  color 
or  form.  It  may  be  bent  as  soon  as  it  yields  in  the  hands,  but  can 
be  drawn  out  only  when  much  hotter  than  this.  Glass  tubing,  how- 
ever, should  not  be  bent  at  too  low  a  temperature ;.  the  curves  made 
at  too  low  a  heat  are  apt  to  be  flattened,  of  unequal  thickness  on  the 
convex  and  concave  sides,  and  brittle. 

In  bending  tubing  to  make  gas-delivery  tubes  and  the  like,  atten- 
tion should  be  paid  to  the  following  points  :  1st,  the  glass  should  be 
equally  hot  on  all  sides ;  2d,  it  should  not  be 

twisted,  pulled  out,  or  pushed  together  dur-  Fig.  32. 

ing  the  heating ;  3d,  the  bore  of  the  tube  at 
the  bend  should  be  kept  round,  and  not 
altered  in  size ;  4th,  if  two  or  more  bends  b  e 
made  in  the  same  piece  of  tubing  (Fig.  32,  a), 
they  should  all  be  in  the  same  plane,  so 
that  the  finished  tube  will  lie  flat  upon  the  level  table. 

When  a  tube  or  rod  is  to  be  bent  or  drawn  close  to  its  extremity, 
a  temporary  handle  may  be  attached  to  it  by  softening  the  end 
of  the  tube  or  rod,  and  pressing  against  the  soft  glass  a  fragment 
of  glass  tube,  which  will  adhere  strongly  to  the  softened  end. 
The  handle  may  subsequently  be  removed  by  a  slight  blow,  or  by 
the  aid  of  a  file.  If  a  considerable  bend  is  to  be  made,  so  that  the 
angle  between  the  arms  will  be  very  small  or  nothing,  as  in  a 
siphon,  for  example,  the  curvature  cannot  be  well  produced  at  one 
place  in  the  tube,  but  should  be  made  by  heating,  progressively, 
several  centimetres  of  the  tube,  and  bending  continuously  from  one 
end  of 'the  heated  portion  to  the  other  (Fig.  32,  6).  Small  and  thick 
tube  may  be  bent  more  sharply  than  large  or  thin  tube. 


xxxviii  MANIPULATION  OF  GLASS.  §  85 

A  lamp  for  bending  glass  tubing  better  than  the  ordinary  form  of 
the  Bunsen  burner,  is  one  the  tube  of  which  is  flattened  out  so  as  to 
give  a  thin  but  broad  flame  of  the  same  character  as  the  ordinary 
lamp  but  in  shape  more  like  a  bat- wing  burner. 
(See  Fig.  33.)    The  tube  is  placed  in  this  flame 
and  turned  round  and  round  until  it  reaches  the 
proper  temperature;   it  is  then  withdrawn  from 
the  flame  and  bent.     In  this  way  a  regular  curve 
may  be  obtained  and  the  sides  of  the  tube  do  not 
collapse. 

In  order  to  draw  a  glass  tube  down  to  a  finer 
bore,  it  is  simply  necessary  to  thoroughly  soften  on 
all  sides  one  or  two  centimetres'  length  of  the  tube 
and  then  taking  the  glass  from  the  flame,  pull  the 
parts  asunder  by  a  cautious  movement  of  the  hands. 
The  larger  the  heated  portion  of  glass,  the  longer 
will  be  the  tube  thus  formed.  Its  length  and  fineness  also  increase 
with  the  rapidity  of  motion  of  the  hands.  If  it  is  desirable  that  the 
finer  tube  should  have  thicker  walls  in  proportion  to  its  bore  than 
the  original  tube,  it  is  only  necessary  to  keep  the  heated  portion  soft 
for  two  or  three  minutes  before  drawing  out  the  tube,  pressing  the 
parts  slightly  together  the  while.  By  this  process  the  glass  will  be 
thickened  at  the  hot  ring. 

To  obtain  a  tube  closed  at  one  end,  it  is  best  to  take  a  piece  of 
tubing,  open  at  both  ends,  and  long  enough 
to  make  two  closed  tubes.  In  the  middle 
of  the  tube  a  ring  of  glass,  as  narrow  as  pos- 
sible, must  be  made  thoroughly  soft.  The 
hands  are  then  separated  a  little,  to  cause 
a  contraction  in  diameter  at  the  hot  and 
soft  part.  The  point  of  the  flame  must  now 

be  directed,  not  upon  the  narrowest  part  of  the  tube,  but  upon 
what  is  to  be  the  bottom  of  the  closed  tube.  This  point  is  indi- 
cated by  the  line  a  in  Fig  34.  By  withdrawing  the  right  hand, 
the  narrow  part  of  the  tube  is  attenuated,  and  finally  melted  off, 
leaving  both  halves  of  the  original  tube  closed  at  one  end,  but  not 
of  the  same  form ;  the  right-hand  half  is  drawn  out  into  a  long 
point,  the  other  is  more  roundly  closed.  It  is  not  possible  to  close 
handsomely  the  two  pieces  at  once.  The  tube  is  seldom  perfectly 
finished  by_the  operations;  a  superfluous  knob  of  glass  generally 
remains  upon  the  end.  If  small  it  may  be  got  rid  of  by  heating  the 
whole  end  of  the  tube,  and  blowing  moderately  with  the  mouth  into 


§86  MANIPULATION  OF  GLASS.  xxxix 

the  open  end.  The  knob,  being  hotter,  and  therefore  softer  than 
any  other  part,  yields  to  the  pressure  from  within,  spreads  out  and 
disappears.  If  the  knob  is  large,  it  may  be  drawn  off  by  sticking 
to  it  a  fragment  of  tube,  and  then  softening  the  glass  above  the 
junction.  The  same  process  may  be  applied  to  the  too  pointed  end 
of  the  right-hand  half  of  the  original  tube,  or  to  any  misshapen 
result  of  an  unsuccessful  attempt  to  close  a  tube,  or  to  any  bit  of 
tube  which  is  too  short  to  make  two  closed  tubes.  When  the 
closed  end  of  a  tube  is  too  thin,  it  may  be  strengthened  by  keep- 
ing the  whole  end  at  a  red  heat  for  two  or  three  minutes,  turn- 
ing the  tube  constantly  between  the  fingers.  It  may  be  said 
in  general  of  all  the  preceding  operations  before  the  lamp,  that 
success  depends  on  keeping  the  tube  to  be  heated  in  constant 
rotation,  in  order  to  secure  a  uniform  temperature  on  all  sides  of 
the  tube. 

86.    Blowing  Bulbs.  —  Bulb-tubes,  like  the  one  represented  in 
Fig.  35,  are  employed  for  reducing  substances  capable  of  forming 
sublimates  upon  the  cold  walls  of 
the  tube.     They  are  readily  made  Fig.  35. 

fiom  bits  of  tubing,  in  the  flame  of 
Bunsen's  burner,  or  in  the  common 
blowpipe  flame. 

If  the  bulb  desired  is  large  in 
proportion  to  the  size  of  the  tube 
on  which  it  is  to  be  made,  the  walls 

of  the  tube  must  be  thickened  by  rotation  in  the  flame  before  the 
bulb  can  be  blown.  The  thickened  portion  of  glass  is  then  to  be 
heated  to  a  cherry-red,  suddenly  withdrawn  from  the  flame,  and 
expanded  while  hot  by  steadily  blowing,  or  rather  pressing  air, 
into  the  tube  with  the  mouth ;  the  tube  must  be  constantly  turned 
on  its  axis,  not  only  while  in  the  flame,  but  also  while  the  bulb  is 
being  blown.  If  too  strong  or  too  sudden  a  pressure  be  exerted 
with  the  mouth,  the  bulb  will  be  extremely  thin  and  quite  useless. 
By  watching  the  expanding  glass,  the  proper  moment  for  arresting 
the  pressure  may  usually  be  determined.  If  the  bulb  obtained  be 
not  large  enough,  it  may  be  reheated  and  enlarged  by  blowing  into 
it  again,  provided  that  a  sufficient  thickness  of  glass  remain. 
If  a  bulb  is  to  be  blown  in  the  middle  of  a  piece  of  tubing,  the 
thickening  is  effected  by  gently  pressing  the  ends  of  the  tube  to- 
gether while  the  glass  is  red-hot  in  the  place  where  the  bulb  is 
to  be. 

It  is  sometimes  necessary  to  make  a  hole  in  the  side  of  a  tube  or 


xl  CAOUTCHOUC.  §  87 

other  thin  glass  apparatus.  This  may  be  done  by  directing  a  pointed 
flame  from  the.  blast-lamp  upon  the  place  where  the  hole  is  to  be, 
until  a  small  spot  is  red-hot,  and  then  blowing  forcibly  into  one  end 
of  the  tube  while  the  other  end  is  closed  by  the  finger ;  at  the  hot 
spot  the  glass  is  blown  out  into  a  thin  bubble,  which  bursts  or 
may  be  easily  broken  off,  leaving  an  aperture  in  the  side  of  the 
tube. 

It  is  hoped  that  these  few  directions  will  enable  the  attentive 
student  to  perform,  sufficiently  well,  all  the  manipulations  with 
glass  tubes  which  the  experiments  described  in  this  manual  re- 
quire. Much  practice  will  alone  give  a  perfect  mastery  of  the  de- 
tails of  glass-blowing. 

87.  Caoutchouc. — Vulcanized  caoutchouc  is  a  most  useful 
substance  in  the  laboratory,  on  account  of  its  elasticity  and  because 
it  resists  so  well  most  of  the  corrosive  substances  with  which  the 
chemist  deals.  It  is  used  in  three  forms  :  (1)  in  tubing  of  various 
diameters  comparable  with  the  sizes  of  glass  tubing ;  (2)  in  stop- 
pers of  various  sizes  to  replace  corks ;  (3)  in  sheets.  Caoutchouc 
tubing  may  be  used  to  conduct  all  gases  and  liquids  which  do  not 
corrode  its  substance,  provided  that  the  pressure  under  which  the 
gas  or  liquid  flows  be  not  greater,  or  their  temperature  higher, 
than  the  texture  of  the  tubing  can  endure.  The  flexibility  of  the 
tubing  is  a  very  obvious  advantage  in  a  great  variety  of  cases. 
Short  pieces  of  such  tubing,  a  few  centimetres  in  length,  are  much 
used,  under  the  name  of  connectors,  to  make  flexible  joints  in  ap- 
paratus, of  which  glass  tubing  forms  part ;  flexible  joints  add  greatly 
to  the  durability  of  such  apparatus,  because  long  glass  tubes  bent 
at  several  angles  and  connected  with  heavy  objects,  like  globes, 
bottles  or  flasks  full  of  liquid,  are  almost  certain  to  break  even  with 
the  most  careful  usage;  gas  delivery-tubes,  and  all  considerable 
lengths  of  glass  tubing  should  invariably  be  divided  at  one  or  more 
places,  and  the  pieces  joined  again  with  caoutchouc  connectors. 
The  ends  of  glass  tubing  to  be  thus  connected  should  be  squarely 
cut,  and  then  rounded  in  the  lamp,  in  order  that  no  sharp  edges 
may  cut  the  caoutchouc ;  the  internal  diameter  of  the  caoutchouc 
tube  must  be  a  little  smaller  than  the  external  diameter  of  the  glass 
tubes ;  the  slipping  on  of  the  connector  is  facilitated  by  wetting 
the  glass.  In  some  cases  of  delicate  quantitative  manipulations,  in 
which  the  tightest  possible  joints  must  be  secured,  the  caoutchouc 
connector  is  bound  on  to  the  glass  tube  with  a  silk  or  smooth  linen 
string;  the  string  is  passed  as  tightly  as  possible  twice  round 
the  connector  and  tied  with  a  square  knot ;  the  string  should  be 


§  88  CAOUTCHOUC.  —  CORKS.  xli 

moistened  in  order  to  prevent  it  from  slipping  while  the  knot  is 
tying. 

Caoutchouc  stoppers  of  good  quality  are  much  more  durable  than 
corks,  and  are  in  every  respect  to  be  preferred.  The  German  stop- 
pers are  of  excellent  shape  and  quality ;  the  American,  being  chiefly 
intended  for  wine  bottles,  are  apt  to  be  too  conical.  Caoutchouc 
stoppers  can  be  bored,  like  corks  (see  the  next  section),  by  means 
of  suitable  cutters,  and  glass  tubes  can  be  fitted  into  the  holes 
thus  made  with  a  tightness  unattainable  with  corks.  German  stop- 
pers may  be  bought  already  provided  with  one,  two,  and  three  holes. 
It  is  not  well  to  lay  in  a  large  stock  of  caoutchouc  stoppers,  for 
though  they  last  a  long  time  when  in  constant  use,  they  not  infre- 
quently deteriorate  when  kept  in  store,  becoming  hard  and  some- 
what brittle  with  age. 

Pieces  of  thin  sheet  caoutchouc  are  very  conveniently  used  for 
making  tight  joints  between  large  tubes  of  two  different  sizes,  or 
between  the  neck  of  a  flask,  or  bottle,  and  a  large  tube  which  enters 
it,  or  between  the  neck  of  a  retort  and  the  receiver  into  which  it 
enters.  A  sufficiently  broad  and  long  piece  of  sheet  caoutchouc  is 
considerably  stretched,  wrapped  tightly  over  the  glass  parts  adjoin- 
ing the  aperture  to  be  closed,  and  secured  in  place  by  a  string 
wound  closely  about  it  and  tied  with  a  square  knot. 

88.  Corks. — It  is  often  very  difficult  to  obtain  sound,  elastic 
corks  of  fine  grain  and  of  size  suitable  for  large  flasks  and  wicle- 
mouthed  bottles.  On  this  account,  bottles  with  mouths  not  too  large 
to  be  closed  with  a  cork  cut  across  the  grain,  should  be  chosen  for 
chemical  uses,  in  preference  to  bottles  which  require  large  corks  or 
bungs  cut  with  the  grain,  and  therefore  offering  continuous  channels 
for  the  passage  of  gases,  or  even  liquids.  The  kinds  sold  as  cham- 
pagne corks  and  as  satin  corks  for  phials  are  suitable  for  chemical 
use.  The  best  corks  generally  need  to  be  softened  before  using ;  this 
softening  may  be  effected  by  rolling  the  cork  under  aboard  upon  the 
table,  or  under  the  foot  upon  the  clean  floor,  or  by  gently  squeezing 
it  on  all  sides  with  the  well-known  tool  expressly  adapted  for  this 
purpose,  and  thence  called  a  cork-squeezer.  Steaming  also  softens 
the  hardest  corks. 

Cork  must  often  be  cut  with  cleanness  and  precision  ;  a  sharp, 
thin  knife,  such  as  shoemakers  use,  is  desirable  for  this  purpose. 
When  a  cork  has  been  pared  down  to  reduce  its  diameter,  a  flat  file 
may  be  employed  in  finishing;  the  file  must  be  fine  enough  to  leave 
a  smooth  surface  upon  the  cork;  in  filing  a  cork,  a  cylindrical,  not  a 
conical,  form  should  be  aimed  at. 


xlii  CORKS.  §88 

In  boring  holes  through  corks  to  receive  glass  tubes,  a  hollow 
cylinder  of  sheet  brass  sharpened  at  one  end 
Fig.  36.  is  a  very  convenient  tool.     Fig.  36  represents 

a  set  of  such  little  cylinders  of  graduated 
sizes,  slipping  one  within  the  other  into  a 
very  compact  form ;  a  stout  wire  of  the  same 
length  as  the  cylinders,  accompanies  the  set, 
and  serves  a  double  purpose,  —  passed  trans- 
versely through  two  holes  in  the  cap  which 
terminates  each  cylinder,  it  gives  the  hand  a 
better  grasp  of  the  tool  while  penetrating  the 
cork;  and  when  the  hole  is  made,  the  wire 
thrust  through  an  opening  in  the  top  of  the 
cap  expels  the  little  cylinder  of  cork  which 
else  would  remain  in  the  cutting  cylinder  of 
brass.  That  cutter,  whose  diameter  is  next 
below  that  of  the  glass  tube  to  be  inserted 
in  the  cork,  is  always  to  be  selected,  and  if 

the  hole  it  makes  is  too  small,  a  round  file  must  be  used  to  enlarge 
the  aperture ;  the  round  file,  also,  often  comes  in  play  to  smooth  the 
rough  sides  of  a  hole  made  by  a  dull  cork-borer.  A  pair  of  small 
calipers  is  a  very  convenient,  though  by  no  means  essential,  tool  in 
determining  which  size  of  cutter  to  employ.  A  flask  which  presents 
sharp  or  rough  edges  at  the  mouth  can  seldom  be  tightly  corked,  for 
the  cork  cannot  be  introduced  into  the  neck  without  being  cut  or 
roughened;  such  sharp  edges  must  be  rounded  in  the  lamp.  In 
thrusting  glass  tubes  through  bored  corks,  the  following  directions 
are  to  be  observed:  (1.)  The  end  of  the  tube  must  not  present  a 
sharp  edge  capable  of  cutting  the  cork.  (2.)  The  tube  should  be 
grasped  very  close  to  the  cork,  in  order  to  escape  cutting  the  hand 
which  holds  the  cork,  should  the  tube  break ;  by  observing  this  pre- 
caution, the  chief  cause  of  breakage,  viz.,  irregular  lateral  pressure, 
will  be  at  the  same  time  avoided.  (3.)  A  funnel-tube  must  never 
be  held  by  the  funnel  in  driving  it  through  a  cork,  nor  a  bent  tube 
grasped  at  the  bend,  unless  the  bend  comes  immediately  above  the 
cork.  (4.)  If  the  tube  goes  very  hard  through  the  cork,  the  appli- 
cation of  a  little  soap  and  water  will  facilitate  its  passage,  but  if 
soap  is  used,  the  tube  can  seldom  be  withdrawn  from  the  cork  after 
the  latter  has  become  dry.  (5.)  The  tube  must  not  be  pushed 
straight  into  the  cork,  but  screwed  in,  as  it  were,  with  a  slow 
rotary  as  well  as  onward  motion.  Joints  made  with  corks  should 
always  be  tested  before  the  apparatus  is  used,  by  blowing  into  the 
apparatus,  and  at  the  same  time  stopping  up'all  legitimate  outlets. 


§89 


GAS-  GENEEA  TOES. 


xliii 


Any  leakage  is  revealed  by  the  disappearance  of  the  pressure  created. 
To  the  same  end,  air  may  be  sucked  out  of  an  apparatus  and  its 
tightness  proved  by  the  permanence  of  the  partial  vacuum.  To  at- 
tempt to  use  a  leaky  cork  is  generally  to  waste  time  and  labor,  and 
to  insure  the  failure  of  the  experiment. 

89.  Gas-bottle.  — Figure  37  represents  a  gas-bottle  fitted  for 
evolving  sulphuretted  hydrogen,  carbonic  acid,  and  other  gases 
which  can  be  prepared  without  heat.  A  straight 
glass  tube  of  convenient  length  is  slipped  into  the 
caoutchouc  connector  at  the  right  to  carry  the  gas 
into  the  solution  to  be  tested.  The  neck  of  the 
bottle  should  be  rather  narrow,  since  it  is  difficult 
to  obtain  tight  stoppers  for  bottles  with  wide 
mouths,  but  must  nevertheless  be  wide  enough  to 
admit  a  cork,  or  better  a  caoutchouc  stopper, 
capable  of  carrying  both  the  delivery  and  the  this- 
tle tubes. 

To  prepare,  for  example,  sulphuretted  hydrogen 
gas,  put  a  tablespoonful  of  fragments  of  sulphide 
of  iron  in  the  bottom  of  the  bottle,  replace  the 
cork  with  its  tubes,  and  press,  or  rather  twist,  it 
tightly  into  the  neck  of  the  bottle ;  pour  in  enough 
water  through  the  thistle-tube  to  seal  the  lower  end  of  that  tube, 
and  finally  as  much  concentrated  sulphuric  acid  as  would  be  equal 
to  a  tenth  or  a  twelfth  of  the  volume  of  the  water. 

At  the  start  it  is  well  thus  to  mix  strong  acid  with  the  water  in 
the  bottle,  for  the  heat  generated  by  the  union  of  the  two  liquids 
serves  to  warm  the  apparatus,  and  to  facilitate  the  decomposition 
of  the  sulphide  of  iron ;  but  it  must  be  remembered  that  strong 
sulphuric  acid  is  by  itself  unfit  for  generating  sulphuretted  hydro- 
gen, and  that  the  evolution  of  gas  would  be  checked  if  much  of  it 
were  added.  When  the  flow  of  gas  ceases,  pour  a  small  portion  of 
dilute  sulphuric  acid  into  the  thistle-tube,  and  repeat  this  operation 
as  often  as  may  be  necessary  to  maintain  a  constant  stream  of  gas. 
Dilute  acid  fit  for  this  purpose  may  be  prepared  by  mixing  1  volume 
of  strong  sulphuric  acid  with  14  volumes  of  water;  —  the  water 
should  be  well  stirred  and  the  acid  poured  into  it  in  a  fine  stream. 

In  precipitating  the  members  of  Classes  II  and  III  with  sulphur- 
etted hydrogen,  the  gas  delivery-tube  should  not  dip  deeper  than 
about  an  inch  beneath  the  surface  of  the  liquid  in  the  beaker.  A 
rapid  current  of  gas  is  useless  and  wasteful.  The  best  method  of 
operating  is  to  pour  dilute  sulphuric  acid  into  the  thistle-tube  in 
15 


xliv 


GAS-  GENERA  TOES. 


§90 


such  quantity  that  the  bubbles  of  gas  may  follow  one  another 
slowly  enough  to  be  counted  without  effort. 

90.  Self-regulating  Gas-generator.  —  An  apparatus  which 
is  always  ready  to  deliver  a  constant  stream  of  sulphuretted  hydro- 
gen, and  yet  does  not  generate  the  gas  except  when  it  is  imme- 
diately wanted  for  use,  is  a  great  convenience  in  an  active  labora- 


Fig.  38. 


tory.  The  same  remark  applies  to  the 
two  gases,  hydrogen  and  carbonic  acid, 
which  are  likewise  used  in  considerable 
quantities  in  quantitative  analysis,  and 
which  can  be  conveniently  generated  in 
precisely  the  same  form  of  apparatus 
which  is  advantageous  for  sulphuretted 
hydrogen.  Such  a  generator  may  be 
made  of  divers  dimensions.  The  fol- 
lowing directions,  with  the  accompany- 
ing figure  (Fig.  38),  will  enable  the 
student  to  construct  an  apparatus  of 
convenient  size.  Procure  a  glass  cylin- 
der 20  or  25  c.  m.  in  diameter  and  30  or 
35  c.  m.  high;  ribbed  candy  jars  are 
sometimes  to  be  had  of  about  this  size ; 
procure  also  a  stout  tubulated  bell-glass 
10  or  12  c.  m.  wide  and  5  or  7  c.  m.  shorter  than  the  cylinder.  Get 
a  basket  of  sheet-lead  7.5  c.  m.  deep  and  2.5  c.  m.  narrower  than 
the  bell-glass,  and  bore  a  number  of  small  holes  in  the  sides  and 
bottom  of  this  basket.  Cast  a  circular  plate  of  lead  7  m.  m.  thick 
and  of  a  diameter  4  c.  m.  larger  than  that  of  the  glass  cylinder;  on 
what  is  intended  for  its  under  side  sokler  three  equidistant  leaden 
strips,  or  a. continuous  ring  of  lead,  to  keep  the  plate  in  proper  posi- 
tion as  a  cover  for  the  cylinder.  Fit  tightly  to  each  end  of  a  good 
brass  gas-cock  a  piece  of  brass  tube  8  c.  m.  long,  1.5  to  2  c.  m.  wide, 
and  stout  in  metal.  Perforate  the  centre  of  the  leaden  plate,  so  that 
one  of  these  tubes  will  snugly  pass  through  the  orifice,  and  secure 
it  by  solder,  leaving  5  c.  m.  of  the  tube  projecting  below  the  plate. 
Attach  to  the  lower  end  of  this  tube  a  stout  hook  on  which  to  hang 
the  leaden  basket.  By  means  of  a  sound  cork  and  common  sealing- 
•wax,  or  a  cement  made  of  oil  mixed  with  red  and  white  lead,  fasten 
this  tube  into  the  tubulure  of  the  bell-glass  air-tight,  and  so  firmly 
that  the  joint  will  bear  a  weight  of  several  pounds.  Hang  the 
basket  by  means  of  copper  wire  within  the  bell  5  c.  m.  above  the 
bottom  of  the  latter.  To  the  tube  which  extends  above  the  stop- 


§  91  MORTARS.  Xlv 

cock  attach  by  a  good  cork  the  neck  of  a  tubulated  receiver  of  100 
or  150  c.  c.  capacity,  the  interior  of  which  has  been  loosely  stuffed 
with  cotton.  Into  the  second  tubulure  of  the  receiver  fit  tightly  the 
delivery- tube  carrying  a  caoutchouc  connector;  ttito  this  connector 
can  be  fitted  a  tube  adapted  to  convey  the  gas  in  any  desired  direc- 
tion. When  many  persons  use  the  same  generator,  each  person 
must  bring  his  own  tube. 

To  charge  the  apparatus,  fill  the  cylinder  with  dilute  acid  to  within 
10  or  12  c.  m.  of  the  top,  fill  the  basket  with  fragments  of  sulphide 
of  iron,  hang  the  basket  in  the  bell,  and  put  the  bell-glass  full  of  air 
into  its  place  with  the  stop-cock  closed.  On  opening  the  cock,  the 
weight  of  the  acid  expels  the  air  from  the  bell,  the  acid  comes  in 
contact  with  the  solid  iii  the  basket,  and  a  steady  supply  of  gas  is 
generated  until  either  the  acid  is  saturated  or  the  solid  dissolved ;  if 
the  cock  be  closed,  the  gas  accumulates  in  the  bell,  and  pushes  the 
acid  below  the  basket  so  that  all  action  ceases.  In  cold  weather 
the  apparatus  must  be  kept  in  a  warm  place.  For  generating  sul- 
phuretted hydrogen,  sulphuric  acid  diluted  with  fourteen  parts  of 
water  is  used;  for  hydrogen,  zinc  and  sulphuric  acid  diluted  with 
four  or  five  parts  of  water;  while  for  carbonic  acid,  chalk  and  muri- 
atic acid  diluted  with  two  or  three  parts  of  water,  should  be  taken. 

91.  Mortars.  — Whenever  the  substance  to  be  analyzed  occurs 
in  the  form  of  large  pieces  or  coarse  powder,  it  should,  as  a  general 
rule,  be  pulverized  by  mechanical  means  before  subjecting  it  to  the 
action  of  solvents.  Mortars  of  iron,  steel,  agate  or  porcelain  are 
used  for  this  purpose,  according  to  the  character  of  the  substance 
to  be  powdered. 

An  iron  mortar  is  useful  -for  coarse  work  and  for  effecting  the  first 
rough  breaking  up  of  substances  which  are  subsequently  powdered 
in  the  agate  or  porcelain  mortar.  If  there  be  any  risk  of  fragments 
being  thrown  out  of  the  mortar,  it  should  be  covered  with  a  cloth  or 
piece  of  stiff  paper,  having  a  hole  in  the  middle  through  which  the 
pestle  may  be  passed.  Instead  of  the  common  iron  mortar,  a  small 
steel  mortar,  of  the  kind  called  diamond  mortars  by  dealers  in  chem- 
ical ware,  may  be  used  for  crushing  minerals.  Pieces  of  stone, 
minerals,  and  lumps  of  brittle  metals  may  be  safely  broken  into 
fragments  suitable  for  the  mortar  by  wrapping  them  in  strong 
paper,  laying  them  so  enclosed  upon  an  anvil  and  striking  them 
with  a  heavy  hammer.  The  paper  envelope  retains  the  broken  par- 
ticles which  might  otherwise  fly  about  in  a  dangerous  manner,  and 
be  lost. 

The  best  porcelain  mortars  are  those  knpwn  by  the  name  of 


MOBTAES.  —  SPA  TULJE.  §§91,92 

Wedge  wood- ware,  but  there  are  many  cheaper  substitutes.  Porce- 
lain mortars  will  not  bear  sharp  and  heavy  blows ;  they  are  intended 
rather  for  grinding  or  triturating  saline  substances  than  for  ham- 
mering; the  pestle  may  either  be  formed  of  one  piece  of  porcelain, 
or  a  piece  of  porcelain  cemented  to  a  wooden  handle ;  the  latter  is 
the  less  desirable  form  of  pestle.  Unglazed  porcelain  mortars  are 
to  be  preferred.  In  selecting  mortars,  the  following  points  should 
be  attended  to,  —  1st,  the  mortar  should  not  be  porous ;  it  ought 
not  to  absorb  strong  acids  or  any  colored  fluid,  even  if  such  liquids 
be  allowed  to  stand  for  hours  in  the  mortar;  2d,  it  should  be  very 
hard,  and  its  pestle  should  be  of  the  same  hardness ;  3d,  it  should 
be  sound;  4th,  it  should  have  a  lip  for  the  convenience  of  pouring 
out  liquids  and  fine  powders.  As  a  rule,  porcelain  mortars  will  not 
endure  sudden  changes  of  temperature.  They  may  be  cleaned  by 
rubbing  in  them  a  little  sand  soaked  in  nitric  or  sulphuric  acid,  or 
if  acids  are  not  appropriate,  in  caustic  soda. 

Agate  mortars  are  only  intended  for  trituration ;  a  blow  would 
break  them.  They  are  exceedingly  hard,  and  impermeable.  The 
material  is  so  precious  and  so  hard  to  work,  that  agate  mortars  are 
always  small.  The  pestles  are  generally  inconveniently  short,  —  a 
difficulty  which  may  be  remedied  by  fitting  the  agate  pestle  into  a 
wooden  handle. 

In  all  grinding  operations  in  mortars,  whether  of  porcelain  or 
agate,  it  is  expedient  to  put  only  a  small  quantity  of  the  substance 
to  be  powdered  into  the  mortar  at  once.  The  operation  of  powder- 
ing will  be  facilitated  by  sifting  the  matter  as  fast  as  it  is  powdered, 
returning  to  the  mortar  the  particles  which  are  too  large  to  pass 
through  the  sieve. 

92.  Spatulse.  —  For  transferring  substances  in  powder,  or  in 
small  grains  or  crystals,  from  one  vessel  to  another,  spatulae  and 
scoops  made  of  horn  or  bone  are  convenient  tools.  A  coarse  bone 
paper-knife  makes  a  good  spatula  for  laboratory  use.  Cards,  free 
from  glaze  and  enamel,  are  excellent  substitutes  for  spatulae. 


INDEX. 


ACETATE  OF  LEAD,  as  reagent,  vii. 
sodium,  as  reagent,  v. 
Acetates,  tests  for,  87. 
Acetic  acid,  as  reagent,  ii. 
Acid,  solutions,  103, 105. 
Alcohol,  as  reagent,  ix. 
Alkaline  solutions,  103. 
Aluminates,      precipitated      with 

Class  IV,  37. 
Aluminum,  confirmatory  test  for, 

41. 
a  member  of  Class  IV, 

11,  37. 
precipitated  as  hydrate, 

11,38. 

Ammonia-water,  as  reagent,  iii. 
Ammonium-salts,  testing  for,   92, 

126. 

Antimony,  confirmatory  test  for,  33. 
converted  into  an  insol- 
uble oxide  by  HNO3, 
31,  123. 

see  sulphide  of. 
globule,  brittle,  95. 
a  member  of  Class  III, 

10,  29. 
precipitated  as  sulphide. 

10,  29. 
presence    of   indicated, 

105. 
spots  distinguished  from 

arsenic  spots,  33. 
ter oxide  of,  as  a  subli- 
mate, 93. 
Aqua  regia,  how  prepared,  ii. 

its  use  as  a  solvent,  101. 
Argand  spirit-lamp,  xxviii. 
Arseniates,  test  for,  78. 
Arsenic,  confirmatory  test  for,31, 32. 
a  member  of  Class  III,  10, 

29. 

presence  of  indicated,  35. 
see  sulphide  of. 
separation  as  sulphide,  10, 

29. 

as  a  sublimate,  93. 
Arsenic  acid,  tests  for,  31,  78. 


Arsenious  acid,  how  distinguished 
from  arsenic 
acid,  78. 

as  a  sublimate,  93. 
tests  for,  78. 
Arsenites,  tests  for,  78. 
Ash  of  charcoal,  95. 

BARIUM,  a  member  of  Class  VI,  13, 

53. 
precipitated  as  carbonate, 

13,  53. 
precipitated  as  chromate, 

54. 
salts  soluble  in  aminonia- 

cal  solutions,  09. 
test  for  certain  classes  of 

salts,  67. 
Beakers,  xv. 

Biborate  of  sodium,  as  reagent,  v. 
Bichloride  of  platinum,  as  reagent, 

how  prepared,  viii. 
Bichromate  of  potassium,  as  rea- 
gent, vi. 

Bismuth,  confirmatory  test  for,  24. 
globule,  brittle,  95. 
a  member  of  Class  II,  9, 

21. 
precipitated  as  hydrate, 

24. 
precipitated  as  sulphide, 

9,21. 
presence  of  indicated,  28, 

105. 

Blast-lamps,  xxv. 
Blowers,  xxvi. 
Blowing  bulbs,  xxxix. 
Blowpipe,  xxx. 

how  to  use,  xxxi. 
lamp,  xxx. 

Boracic  acid,  precipitated  from  an 
alkaline  solution, 
104. 

tests  for,  81. 
Borates,  tests  for,  81. 
Borax-bead,  how  to  dilute,  113. 
"    "  make,  113. 


xlviii 


INDEX. 


Bottles,  how  to  handle,  xiii. 
Bromides,  tests  for,  84. 
Bromine,  tests  for,  84. 
Bunsen's  burner,  xxiv. 

filter-pump,  xx. 

CADMIUM,  a  member  of  Class  H, 

9,  24. 
precipitated  as  sulphide, 

presence  of  indicated,  27. 
separation  of,  24. 
Calcium,  a  member  of  Class  VI, 

13,  53. 
precipitated  as  carbonate, 

13,  53. 
precipitated   as   oxalate, 

55. 
tests  for  certain  classes 

of  salts,  70. 
Caoutchouc  stoppers,  xli. 

tubing,  xl. 

Carbonate   of    ammonium,   as  re- 
agent, iii. 
Carbonate  of  sodium,  as  reagent, 

how  purified,  v. 
Carbonates,  tests  for,  75. 
Carbonic  acid,  tests  for,  75. 
Caustic  soda  solution,  how  prepared 

and  kept,  iv. 

Charcoal  for  blowpipe  use,  94. 
Chlorates,  tests  for,  86. 
Chloride  of  ammonium,  reagent,  iv. 
uses  of,  11, 

45,  57. 

Chloride  of  barium,  as  reagent,  vii. 
Chloride   of  calcium,  as  reagent, 

how  prepared,  vii. 
Chloride  of  lead,  solubility  of,  10. 
Chloride  of  mercury,  as  reagent, 

viii. 

Chloride  of  silver  soluble  in  ammo- 
nia-water, 18. 
Chlorides,  tests  for,  71,  83. 
Chlorhydric  acid,  as  reagent,  i. 

its  application  as 

a  solvent,  99. 
Chlorine,  tests  for,  71,  83. 
Chromate  of  lead,  a  test  for  chro- 
mium, 40. 
Chromate   of  potassium,   reagent, 

vi. 
Chromates,  barium  test  for,  68. 

reduction  of  by  H2S, 

28,  77. 
tests  for,  77. 

Chrome-iron-ore,    hard  to  decom- 
pose, 114. 

Chromic-oxide,  hard  to  decompose, 
114. 


Chromites,  precipiated  with  Class 

IV,  37. 

Chromium,  a  member  of  Class  IV, 
11,  37. 

detected    as   chromate 

of  sodium,  40. 
gives    a   green    borax- 
bead,  114. 
precipitated  as  hydrate, 

11,  37. 
presence  of  indicated, 

46. 

Class,  term  defined,  5. 
Class  I,  defined,  6. 

how  to  precipitate,  17. 
Class  II,  defined,  7. 

how  to  precipitate,  21. 
Class  III,  defined,  7. 
Class  III,  precipitation  of,  29. 
Class  IV,  defined,  10. 

how  to  precipitate,  38,  45. 
salts    precipitated   with, 

37. 
Class  V,  defined,  12. 

how  to  precipitate,  47,  52. 
Class  VI,  defined,  13. 

how  to  precipitate,  53, 57. 
Class  VII,  defined,  13. 

how  isolated,  14,  61. 
Clay  chimney  for  Bunsen's  burner, 

xxviii. 

Closed-tube  test,  90. 
Cobalt,  member  of  Class  V,  12,  47. 
blowpipe  test  for,  49. 
confirmatory  test  for,  50. 
precipitated  as  sulphide,  12, 

47. 

presence  of  indicated,  52. 
Copper,  member  of  Class  II,  9,  21. 
confirmatory  test  for,  26. 
gives  blue  solutions,  24. 
globule  described,  95,  96. 
precipitated  as  sulphide,  9, 

21. 

presence  of  indicated,  28. 
Cork-cutters,  xlii. 
Corks,  xli. 

to  force  tubes  through,  xlii. 
Cyanide  of  mercury,  to  detect  cya- 
nogen in,  76. 

Cyanide  of  potassium,  reagent,  vi. 
Cyanides,  tests  for,  74,  75. 
Cyanogen,  tests  for,  74,  75. 

DEFLAGRATION",  119. 
Dissolving  in  acids,  99. 
in  water,  99. 

EFFERVESCENCE,  what  it  indicates, 
74. 


INDEX. 


xlix 


Elements,  identified  by  compounds, 
2. 

Elements,  34  treated  of,  1. 

Etching  glass,  a  test  for  fluorine,82. 

Evaporation  test,  applied  to  a  li- 
quid, 125. 

FERRI-  and  FERRO-CYANIDES  of  po- 
tassium, as  reagents,  vi. 

Ferric  chloride,  as  reagent,  viii. 

Filtering,  xv. 

Filter-stand,  xyii. 

Filtration,  rapid,  xviii. 

Flasks,  xv. 

Fluoride  of  silicon,  a  test  for  fluo- 
rine and  silicon,  83. 

Fluorides,  tests  for,  82. 

Fluorine,  tests  for,  82. 

to  be  sought  in  an  insolu- 
ble mineral,  114,  117. 

Folding  filters,  xvi. 

Funnels,  xv. 

Fused,  minerals,  how  treated,  115. 

Fusion  with   acid  sulphate  of  so- 
dium, 119. 

with  CaCO3  and  N  H4C1, 118. 
with  carbonate  of  sodium,  114. 

Fusions  in  platinum  crucibles, 
xxvii. 

GAS-BOTTLE,  xliii. 
Gas-generator,  self-regulating,  xliv. 
General  reagent,  defined,  6. 
General  reagents  for  acids,  66. 
General  reagents  to  be  used  in  a 

certain  order,  16. 

Glass,  bending  and  closing  tubes, 
xxxvi. 

cutting  and  cracking  it,  xxxv. 

tubing,  xxxiv. 
Gold  globule,  described,  95,  96. 

insoluble  in  HNOa,  123. 

a  member  of  Class  III,  10,  29. 

presence  of  indicated,  35. 

purple  of  Cassius  test  for,  123. 

HYDROGEN,  its  presence  inferred, 

64. 

Hyponitric  acid,  92. 
Hyposulphites,  tests  for,  77. 

INDIGO  SOLUTION,  how  prepared,  ix. 

Insoluble  substances,  110. 

Iodides,  tests  for,  85. 

Iodine,  tests  for,  85. 

lodo-starch  paper,  vii. 

Iron,  discrimination  between  fer- 
rous and  ferric  salts,  44. 

Iron,  to  be  converted  into  ferric 
salt,  44. 


Iron,  a  member  of  Class  IV,  11,  37. 

precipitated  as  hydrate,  11, 37. 

presence  of  indicated,  46. 

Prussian  blue  test  for,  42. 

reaction  in  borax  bead,  114. 
Iron  stand,  xxviii. 

LABELLING,  importance  of,  8. 

Lamps,  xxiii. 

Lead,  belongs  to  two  classes,  10. 

globule  described,  95. 
Lead  a  member  of  Class  I,  6,  17. 
"   11,9,21. 

paper,  how  prepared,  vii. 
precipitated  as  sulphide,  9, 21. 
precipitation  as  chloride,  17. 
precipitation  as  sulphate,  18, 

23. 

presence  of  indicated,  27. 
the  sulphate  changed  to  chro- 

mate,  23. 

Lime-water,  as  reagent,  vii. 
Liquids  to  be  tested  with  litmus. 

125. 
Litmus  paper,  how  prepared,  ix. 

MAGNESIUM,  as  member  of  Class 

VII,  13,  59. 

Magnesium,  precipitated  as  phos- 
phate of   Mg  and 
NH4,  14,  59. 
•  separation  as  oxide, 

61. 

Manganate  of  sodium,  42. 
Manganese,  confirmatory  test,  42. 

precipitated  with  Class 

IV,  37. 

precipitation  of,  as  hy- 
drate, 48. 

presence  indicated,  62. 
Mercuric  chloride,  as  reagent,  viii. 
Mercurous  chloride,  reaction  with 

ammonia-water,  19. 
Mercury,  belongs  to  two  classes,  10. 
compounds  as  sublimates, 

92. 

member  of  Class  I,  6, 17. 
menlber  of  Class  II,  9,  21. 
precipitation  as  subchlor- 

ide,  17. 

presence  of  indicated,  27. 
reduction  of  the  metal  in 

a  closed  tube,  19. 
reduction  of  the  metal  on 

copper,  23. 
separation  as  sulphide.  9, 

21. 

as  a  sublimate,  92. 
Metallic  elements,  7  classes  of,  15. 
globules  described,  94. 


INDEX. 


Metal  lie  globules  tested  in  oxidizing 
flame,  i)5. 

Metals,  action  of  HNO3  on,  121. 
used  in  the  arts,  121. 

Molybdate   of  ammonium,  a  test 
for  phosphates,  79. 

Molybdate  of  ammonium,  as   re- 
agent, how  prepared,  iv. 

Mortars  xlv. 

NEUTRAL  SOLUTIONS,  103. 
Nickel,  blowpipe  test  for,  49. 

member  of  Class  V,  12,  47. 
precipitated  as  cyanide,  50. 
precipitated  as  sulphide,  12, 

47. 

presence  of  indicated,  52. 
Nitrate  of  barium,  as  reagent,  vii. 
when  used,  69. 

Nitrate  of  cobalt,  as  reagent,  viii. 
Nitrate  of  potassium,  as  reagent,  vi. 
Nitrate  of  silver,  as  reagent,  vii. 
Nitrate  of  sodium,  as  reagent,  v. 
Nitrates,  tests  for,  85. 
Nitric  acid,  action  on  metals,  121. 
dilute,  as  reagent,  ii. 
strong,  as  reagent,  ii. 
tests  for,  85. 
when  to  be  used  as  a 

solvent,  99, 100, 121. 
Nitrite  of  potassium,  as  reagent, 

how  prepared,  vi. 

Non-metallic    elements,    how   de- 
tected, 64. 

ORGANIC  MATTER,  detection  of,  91. 

how  destroyed,  97. 

Organic  substances  hinder  the  pre- 

'  cipitation  of  Class  IV,  47. 
Oxalate  of  ammonium,  reagent,  iv. 
Oxalates  converted  into  carbonates, 
56. 

tests  for,  80. 

Oxalates,  acid  as  a  sublimate,  93. 
as  reagent,  ii. 
tests  for,  80. 
Oxide  of  manganese,  as   reagent, 

viii. 

Oxide  of  mercury,  as  reagent,  viii. 
Oxidizing  blowpipe  flame,  viii. 
Oxygen,  how  recognized,  91. 

its  presence  inferred,  64. 

PHOSPHATE  OF  CALCIUM,  presence 

of  indicated,  46. 

Phosphate  of  sodium,  as  reagent,  v. 
Phosphates,  precipitated  with  Class 

Phosphates,  tests  for,  79. 
Phosphoric  acid,  tests  for,  79. 


Pincers,  xxxiii. 

Platinum,  a  member  of  Class  III, 

10,  29. 

crucibles,  xxxiii. 
foil,  xxxii. 

insoluble  in  HNOg,  123. 
presence  of  indicated,  35. 
test  for,  123. 
wire,  xxxiii. 
Porcelain  crucibles,  xxiii. 

dishes,  xxiii. 
Potassium,  precipitated  as  chloro- 

platinate,  60. 
flame-test  for,  60. 
a  member  of  Class  VH, 

13,  59. 
Precipitates  compacted  by  boiling 

and  shaking,  25,  47. 
Preliminary     examination     of     a 

liquid,  125. 
Preliminary  treatment,  90. 

of  a  pure 
metal  or 
alloy,121. 

Proto^hloride  of  tin,  as  reagent,  viii. 
Prussian  blue,  a  test  for  iron,  42. 
Pulverizing,  xlv. 

QUALITATIVE  ANALYSIS  denned,  1. 

REAGENT  BOTTLES,  xiii. 
Reagents,  i-ix. 

Reducing  blowpipe  flame,  xxxii. 
Reduction  test,  81. 

how  to  perform  with 

delicacy,  111. 

Reduction  test,  to  be  applied  to  in- 
soluble substances,  111. 

SALTS,  kinds  of  considered,  65. 

soluble  in  water,  102. 
Sand-bath,  xxix. 
Separation  of  two  elements,  4. 
Silicates,  alkaline,  decomposed  by 
acids,  82,  104. 
decomposed   by 
chloride  of  am- 
monium, 82. 

Silicates,  the  commonest  of  insolu- 
ble substances,  118. 
Silicic  acid,   precipitated  from  an 

alkaline  solution,  104. 
Silver,  a  member  of  Class  I,  6,  17. 
globule  described,  95. 
precipitated     by    reducing 

agents,  73. 

precipitation  as  chloride,  17. 
salts,     insoluble    in    dilute 

nitric  acid,  17. 
salts,  sundry,  colors  of,  72. 


INDEX. 


Ii 


Silver,  see  chloride  of. 

test    for  certain    classes    of 

salts,  71. 

Slaked  lime,  as  reagent,  vii. 
Sodium,   crystallization  of  chloro- 

platinate  of,  61. 
Sodium,  flame-test  for,  GO. 

a    member  of  Class  VII, 

13,  59. 

Solubilities,  Table  of,  108,  109. 
Solution  of  indigo,  as  reagent,  ix. 
Solutions  of  known  composition,  x. 
Solvents,  the  order  of  use,  98. 
Spatulse,  xlvi. 

Special  tests  for  non-metallic  ele- 
ments, 74. 

Starch  paste,  how  prepared,  ix. 
Starch-test  for  bromine,  84. 

iodine,  85. 

Stirring  rods,  xxxiv. 
Stoppers,  stuck,  how  to  loosen,  xiv. 
Strontium,  a  member  of  Class  VI, 

13,  53. 

precipitated   as   carbon- 
ate, 13,  53. 
as   sulphate. 

55. 

Sublimates  on  charcoal  while  re- 
ducing metals,  96. 
Sulphate  of  copper,  as  reagent,  viii. 
Sulphate  of  magnesium,  as  reagent, 

how  mixed,  vii. 

Sulphate  of  magnesium,  a  test  for 
avseniates  and  phosphates,  31,  79. 
Sulphate  of  sodium,  acid,  how  pre- 
pared, v. 

Sulphates,  barium  test  for,  69. 
how  to  detect,  79. 
insoluble,  reduced  to  sul- 
phides, 112. 
Sulphate  of  potassium,  as  reagent, 

how  prepared,  y. 

Sulphide  of  arsenic,  oxidation  of,  30. 
Sulphide  of  tin.  oxidation  of,  30. 
Sulphides,  tests  for,  76. 
Sulphides  of  arsenic,  as  sublimates, 

9:5. 

Sulphites,  tests  for,  76. 
Sulphur,  as  a  sublimate,  92. 
Sulphuretted   hydrogen,       decom- 
posed by  oxidizing  agents,  28. 
Sulphuretted  hydrogen,  how  pre- 
pared, iii. 

Sulphuretted  hydrogen,  how  to  em- 
ploy it,  7,  21. 


Sulphuretted    hydrogen,  necessity 

of  expelling,  45. 
Sulphuretted  hydrogen  water,  how 

prepared  and  kept,  iii. 
Sulphuric  acid,  as  reagent,  ii. 
Sulphuric  acid,  tests  for,  79. 
Sulphurous  acid,  76. 
Sulphur,  precipitation  of,  20,  28. 
Sulphydrate  of  ammonium,  as  re- 
agent, iii. 

sodiiim,       as      re- 
agent, v. 

TABLE  for  Class  1, 19. 

II,  26. 

III,  34. 

IV,  43. 

V,  51. 

VI,  56. 

the  separation  of  the  7 
classes  of  metallic  ele- 
ments, 62. 

Table  of  solubilities,  108,  109. 
Table  of  the  seven  classes  of  metallic 

elements,  15. 
Tartaric  acid,  as  reagent,  ii. 

tests  for,  80. 
Tartrates,  tests  for,  80. 
Test-tube  rack,  xv. 
Test-tubes,  xiv. 

Tin,  a  member  of  Class  IIT,  10,  29. 
confirmatory  test  for,  34. 
converted  into  an  insoluble  ox- 
ide by  HNOs,  31,  123, 
Tin  globule,  described,  95,  96. 
presence  of  indicated,  35. 
reduction  of  by  zinc,  33. 
see  sulphide  of. 
Triangle,  xxix. 
Turmeric  paper,  how  prepared,  81. 

UTENSILS,  list  of,  xii. 

WATER,  ix. 
Water-bath,  xxix. 
Wash-bottle,  xxxiii. 
Wire-gauze,  xxviii. 

ZINC,  a  member  of  Class  V,  12,  47. 
as  reagent,  viii. 
precipitated  as  chromate,  49. 
precipitated  as  sulphide,  12, 

47,  41. 
presence  of  indicated,  52. 


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HARBISON.  The  Mechanics'  Tool  Book,  with  Practical 
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HENRICI  (Olaus).  Skeleton  Structures,  especiaJ^  in  their 
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HEWSON  (Wm.)  Principles  and  Practice  of  Embanking 
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THE  IE  BOULENGE  CHRONOGRAPH.  By  Bvt.  Capt. 
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5 


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HOLLET  (A.  L.)  Railway  Practice.  American  and  Euro- 
pean  Railway  Practice,  in  the  economical  Generation  of 
Steam,  including  the  Materials  and  Construction  of  Coal- 
burning  Boilers,  Combustion,  the  Variable  Blast,  Va- 
porization, Circulation,  Superheating,  Supplying  and 
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and  Coke-burning  Engines  to  Coal-burning;  and  in 
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•  •  •  "All  these  subjects  are  treated  by  thft  author  in  both  an  intelligent  and  Intel 
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pie  style,  accompanied  by  beautiful  engravings,  and  wo  presume  the  work  will  be  r* 
garded  as  indispensable  by  all  who  are  interested  in  a  knowledge  of  the  construction  o< 
railroads  and  rolling  stock,  or  the  working  of  locomotives."—  Scientific  American. 

HUNT  (R.  M.)  Designs  for  the  Gateways  of  the  Southern 
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KING  (W.  H.)  Lessons  and  Practical  Notes  on  Steam, 
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THE  KANSAS  CITY  BRIDGE,  with  an  account  of  the 
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ON  THE   STBENGTH  OF  BBIEGES  AKD  BOOIS  for 

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MINIFIE  (Wm.)  Mechanical  Drawing.  A  Text-Book 
of  Geometrical  Drawing  for  the  use  of  Mechanics  and 
Schools,  in  which  the  Definitions  and  Rules  of  Geometry 
are  familiarly  explained ;  the  Practical  Problems  are  ar- 
ranged, from  the  most  simple  to  the  more  complex,  and 
in  their  description  technicalities  are  avoided  as  much 
as  possible.  With  illustrations  for  Drawing  Plans,  Sec- 
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Introduction  to  Isometrical  Drawing,  and  an  Essay  on 
Linear  Perspective  and  Shadows.  Illustrated  with  over 
200  diagrams  engraved  on  steel.  By  Wm.  Minifie, 
Architect.  Seventh  Edition.  With  an  Appendix  on 
the  Theory  and  Application  of  Colors.  1  vol.  8vo, 
cloth $4  oo 

WILLIAMSON.  Practical  Tables  in  Meteorology  and 
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CULLEY.  A  Hand-Book  of  Practical  Telegraphy.  By 
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POPE.     Modern  Practice  of  the  Electric  Telegraph.     For 
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MINIFIE  (Wm.)  Geometrical  Drawing.  Abridged  from 
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POTTERY,  Materials  and  Manufacture  of  Terra  Gotta, 
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».  TAN  NOBTBAND'S  PUBUCATIONS. 

PIERCE  (Prof.  Bcnj.)  System  of  Analytical  Mechanics. 
Physical  and  Celestial  Mechanics,  by  Benjamin  Pierce, 
Perkins  Professor  of  Astronomy  and  Mathematics  in 
Harvard  University,  and  Consulting  Astronomer  of  the 
American  Ephemeris  and  Nautical  Almanac.  Developed 
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"I  hare  re-examined  the  memoirs  of  the  great  geometers,  and  have  strive:)  to 
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uniform  treatise.  If  I  have  hereby  succeeded  in  opening  to  the  students  of  my  country  * 
readier  access  to  these  choice  jewels  of  intellect;  if  their  brilliancy  is  not  impaired  in  thii 
attempt  to  reset  them;  if,  in  their  own  constellation,  they  illustrate  each  other,  and  con- 
centrate a  stronger  light  upon  tho  names  of  their  discoverers;  and,  still  more,  if  any  gem 
wuich  I  may  have  presumed  to  add  is  not  wholly  lustreless  in  tho  co  lection,  —  I  shall  feef 
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PLYMPTON.  The  Blow-Pipe  ;  a  System  of  Instruction  in 
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Examination  of  Metallic  Combinations.  Second  edi- 
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POOK  (S.  M.)  Method  of  Comparing  the  Lines  and 
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RANDALL'S  QUARTZ  OPERATOR'S  HAND-BOOK.    By 

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ROGERS  (H.  D.)  Geology  of  Pennsylvania.  A  complete 
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D.  TAN  NOSTIUND'S   PUBMOAT1ONB, 

SUBMARINE  BLASTING  IN  BOSTON  HARBOR, 
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of  Engineers,  and  Brevet  Major-General,  United 
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SHAFFNER  (T.  P.)  Telegraph  Manual.  A  complete 
History  and  Description  of  the  Semaphoric,  Electric, 
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with  625  illustrations.  By  Tal.  P.  Shaffner,  of  Ken- 
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SILVERSMITH  (Julius).  A  Practical  Hand-Book  for  Mi- 
ners, Metallurgists,  and  Assay ers,  comprising  the  most 
recent  improvements  in  the  disintegration,  amalgama 
tion,  smelting,  and  parting  of  the  Precious  Ores,  with  a 
Comprehensive  Digest  of  the  Mining  Laws.  Greatly 
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SIMM'S  LEVELLING.  A  Treatise  on  the  Principles  and 
Practice  of  Levelling,  showing  its  application  to  pur- 
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PLATTNER'S  BLOW-PIPE  ANALYSIS.  A  Complete 
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with  the  Blow-Pipe.  Revised  and  enlarged  by  Prof. 
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man edition  by  Henry  B.  Cornwall,  A.  M.,  E.  M. 
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DEIDRICH'S  Theory  of  Strains  for  the  Construction  of 
Bridges,  Roofs  and  Cranes.  Illustrated  with  plates 
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ST1LLMAN  (Paul).  Steam  Engine  Indicator,  and  the 
Improved  Manometer  Steani  and  Vacuum  Gauges — 
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New  edition,  i  vol.  i2mo,  flexible  cloth i.oo 

RANMELSBERG  S  Guide  to  Quantitative  Chemical  An- 
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SWEET  (S.  H  )  Special  Report  on  Coal ;  showing  its 
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York,  and  the  principal  cities  on  the  Atlantic  Coast. 
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INTRODUCTION  TO  CHEMICAL  PHYSICS,  Designed 
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WALKER  (W.  H.)  Screw  Propulsion.  Notes  on  Screw 
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EXAMINATION  OF  THE  TELEGRAPHIC  APPARA- 
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Morse,  LL.D.  8vo,  cloth 3.01- 


D.  VAN  NOSTBAND'S  PUBLICATIONS. 

WEISBACH'S  MECHANICS.  New  and  revised  edition. 
A  Manual  of  the  Mechanics  of  Engineering,  and  of 
the  Construction  of  Machines.  By  Julius  Weisbarh, 
PH.  D.  Translated  from  the  fourth  augmented  and 
improved  German  edition,  by  Eckley  B.  Coxe,  A.  M.f 
Mining  Engineer.  Vol.  I. — Theoretical  Mechanics. 
i  vol.  8vo,  1,100  pages,  and  902  wood-cut  illustra- 
tions, printed  from  electrotype  copies  of  those  of  the 

best  German  edition $10.00 

ABSTRACT  OF  CONTENTS. — Introduction  to  the  Cal- 
culus— The  General  Principles  of  Mechanics — Pho- 
ronomics,  or  the  Purely  Mathematical  Theory  of 
Motion — Statics  of  Rigid  Bodies — The  Application 
of  Statics  to  Elasticity  and  Strength — Dynamics  of 
Rigid  Bodies — Statics  of  Fluids — Dynamics  of  Fluids 
— The  Theory  of  Oscillation,  etc. 

"  The  present  edition  is  au  entirely  new  work,  greatly  extended  and  very  much  im- 
proved. It  forms  a  text-book  which  must  find  its  way  into  the  hands,  not  only  of  every 
student,  but  of  every  engineer  who  desires  to  refresh  his  memory  or  acquire  clear  ideaa 
on  doubtful  points." — The  Technologist. 

WABD  (J.  H.)  Steam  for  the  Million.  A  popular  Trea- 
tise on  Steam  and  its  Application  to  the  useful  Arts, 
especially  to  Navigation.  By  J.  H.  Ward,  Com- 
mander U.  S.  Navy.  New  and  revised  edition,  i 
vol.  8vo,  cloth i .  oo 

WHILDEN  (J.  K.)  On  the  Strength  of  Materials  used 
in  Engineering  Construction.  By  J.  K.  Whilden. 
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WILLIAMSON  (R.  S.)  Un  the  use  of  the  Barometer  on 
Surveys  and  Reconnaissances.  Part  I.  Meteorology 
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rometric Hypsometry.  By  R.  S.  Williamson,  Bvt. 
Lieut. -Col.  U.  S.  A.,  Major  Corps  of  Engineers. 
With  Illustrative  Tables  and  Engravings.  Paper 
No.  15,  Professional  Papers,  Corps  of  Engineers. 

i  vol.  4to,  cloth 15  oo 

11 


D.  VAN  NOSTRAND'S  PUBLICATIONS. 

ROEBLING  (J.  A.)  Long  and  Short  Span  Railway 
Bridges.  By  John  A.  Roebling,  C.  E,  Illustrated 
with  large  copperplate  engravings  of  plans  and  views. 
Imperial  folio,  cloth $2  5 .  co 

CLARKE  (T.  C.)  Description  of  the  Iron  Railway 
Bridge  over  the  Mississippi  River,  at  Quincy,  Illi- 
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Illustrated  with  27  lithographed  plans,  i  vol.  8vo> 
cloth 7  50 

TUNNER  (P.)  A  Treatise  on  Roll-Turning  for  the 
manufacture  of  Iron.  By  Peter  Tunner.  Trans- 
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sylvania Steel  Works,  with  numerous  engravings 
and  wood-cuts,  i  vol.  8vo,  text,  and  fol.  vol.  Plates, 
cloth 10.00 

[SHERWOOD  (B.  F.)  Engineering  Precedents  for  Steam 
Machinery.  Arranged  in  the  most  practical  and 
useful  manner  for  Engineers.  By  B.  F.  Isher- 
wood,  Civil  Engineer,  U.  S.  Navy.  With  illustra- 
tions. Two  volumes  in  one.  8vo,  cloth 2 . 50 

8AUERMAN.  Treatise  on  the  Metallurgy  of  Iron,  con- 
taining outlines  of  the  History  of  Iron  Manufacture, 
methods  of  Assay,  and  analysis  of  Iron  Ores,  pro- 
cesses of  manufacture  of  Iron  and  Steel,  etc.,  etc. 
By  H.  Bauerman.  First  American  edition.  Re- 
vised and  enlarged,  with  an  appendix  on  the  Martin 
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S.  Hewitt  Illustrated  with  numerous  wood  engra- 
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"  This  is  an  important  addition  to  the  stock  of  technical  works  published  In  thte 
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;he  subject,  as  well  as  in  all  technical  and  scientific  libraries."— Scientific  American. 

ELIOT  &  STORER'S  Manual  of  Qualitative  Chemical 
Analysis.  New  edition,  revised.  By  Prof.  W.  R. 

Nichols.     1 2mo,  illustrated 1.5° 

12 


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NUGENT.  Treatise  on  Optics  :  or,  Light  and  Sight,  the- 
oretically and  practically  treated  ;  with  the  applica- 
tion to  Fine  Art  and  Industrial  Pursuits.  By  E. 
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"  Tbts  book  is  of  a  practical  rather  than  a  theoretical  kind,  and  is  designed  to  afford 
accurate  ami  complete  information  to  all  interested  in  applications  of  the  science. — Rounu 
lablt 

8ABINE.  HISTORY  AND  PROGRESS  OF  THE  ELEC- 
TRIC TELEGRAPH.  By  Robert  Sabine,  C.E.  2d 
edition,  with  additions.  Fully  illustrated.  r2mo,  clo.  1.25 

GLYNN  (J.)  Treatise  on  the  Power  of  Water,  as  applied 
to  drive  Flour  Mills,  and  to  give  motion  to  Tur- 
bines and  other  Hydrostatic  Engines.  By  Joseph 
Glynn.  Third  edition,  revised  and  enlarged,  with 
numerous  illustrations.  1 2mo,  cloth i .  25 

PRIME.  TREATISE  ON  ORE  DEPOSITS.  By  Bern- 
hard  Von  Cotta.  Translated  from  the  Second  Ger- 
man edition  by  Frederick  Prime,  Jr.,  Mining  Engi- 
neer, and  revised  by  the  Author.  With  numerous 
illustrations.  Svo,  cloth 4  .  oo 

HUMBER.  A  Handy  Book  for  the  Calculation  of  Strains 
in  Girders  and  similar  Structures,  and  their  Strength, 
consisting  of  Formulae  and  corresponding  Diagrams, 
with  numerous  details  for  practical  application.  By 
William  Humber.  i2mo,  fully  illustrated,  cloth...  2.50 

G1LLMORE.  Engineer  and  Artillery  Operations  against 
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—  Supplementary  Report  to  the  above,  with  7  litho- 
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13 


P.  VAN  NOSTRAND'S  PUBLICATIONS 

AUCHINCLOSS.  Link  and  Valve  Motions  Simplified. 
Illustrated  with  37  wood  cuts,  and  21  lithographic 
plates,  together  with  a  Travel  Scale,  and  numerous 
useful  Tables.  By  W.  S.  Auchincloss.  8vo.,  cloth,  $3  ex 

JOYNSON.    METALS   USED  IN   CONSTRUCTION- 

Iron,  Steel,  Bessemer  Metal,  etc.,  etc.     With  illus- 
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THE  ART  OF  GRAINING.  How  Acquired  and  How 
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VAN  BU&JhiN .  investigations  of  Formulas,  for  the  strength 
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JOYNSON.      Designing  and   Construction  of  Machine 

Gearing.     Illustrated,  8vo.,  cloth, a  oa 

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COIGNET-BETON,  and  other  Artificial  Stone.     By  Q.  A. 

Gillmore.    Illustrated  with  9  Plates.     8vo,  cloth 2. 50* 

FREE  HAND  DRAWING,  a  Guide  to  Ornamental,  Fig- 
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THE  EARTH'S  CRUST.     A  handy  Outline  of  Geology. 

By  David  Page.     Illustrated,  i8mo.,  cloth, 75 

DICTIONARY  of  Manufactures,  Mining,  Machinery,  and 
the  Industrial  Arts.  By  George  Dodd.  iamo., 

Cloth, :'    O'J 

14 


D.  VAN  NOSTRAND'S  PUBLICATIONS 

HURT.  Key  to  the  Solar  Compass,  and  Surveyor's  Com- 
panion. By  W.  A.  Burt.  Second  edition.  Pocket- 
book  form,  tuck $2.50 

A  TREATISE  ON  THE  RICHARDS  STEAM-ENGINE 
INDICATOR,  with  Directions  for  its  Use.  By  Chas. 
T.  Porter.  Revised  with  notes  and  large  additions, 
as  developed  by  American  Practice,  with  an  Appendix 
containing  useful  formulae  and  rules  for  Engineers. 
By  F.  W.  Bacon,  M.  E.,  Member  of  the  American 
Society  of  Civil  Engineers.  1 8  mo,  illustrated.  Cloth,  i.oc 

ON  THE  FILTRATION  OF  RIVER  WATERS,  for  the 

Supply  of  Cities,  as  practised  in  Europe,  made  to  the 
Board  of  Water  Commissioners  of  the  City  of  St. 
Louis.  By  J.  P.  Kirkwood,  Civil  Engineer.  Illus- 
trated by  30  engravings.  4to,  cloth 1 5 .  oo 

THE  PLANE-TABLE  AND  ITS  USE  IN  TOPOGRAPH- 
ICAL  SURVEYING.  From  the  Papers  of  the  U. 
S.  Coast  Survey.  8vo,  illustrated.  Cloth  2 .  oo 

REPORT  on  Machinery  and  Processes  of  the  Industrial 
Arts  and  Apparatus  of  the  Exact  Sciences.  By  F.  A. 
P.  Barnard,  LL.  D.  Paris  Universal  Exposition, 
1867.  i  vol.  8vo,  cloth 5 .00 

IRON  TRUSS   BRIDGES   FOR  RAILROADS.      The 

Method  of  Calculating  Strains  in  Trusses,  with  a 
ICareful  Comparison  of  the  most  Prominent  Trusses  in 
Reference  to  Economy  in  Combination,  etc.  By 
Brevet  Colonel  William  E.  Merrill,  U.  S.  A.  Illus- 
trated. 4to,  cloth 5 .00 

USEFUL    INFORMATION    FOR    RAILWAY    MEN. 

By  W.  G.  Hamilton,  Engineer.  Fourth  edition,  re- 
vised and  enlarged.  600  pp.  Morocco  gilt.  For 

pocket j.cy 

15 


VAN  NOSTRAND'S 

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112  PAGES,  LARGE  8vo,  MONTHLY. 

First  Number  was  Issued  Jan.  i,  1869 

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